I've been wondering about the situation with regard to elf mages during the Long March. Did they only come from the ranks of children of liberated parents or did elves who had received training from Tevinter humans comprise the first wave? Currently if someone demonstrates magical ability in Tevinter they are immediately elevated above the ranks of non-mages, even non-mage nobility. Has that always been the case? So would an elf mage identify more with non-mage elves or human mages? The Canticle of Shartan describes his elves using bows in the battle and other texts mention how they made weapons from anything they could get hold of. Naturally I suppose any reference to elf mages assisting in the fight would have been expunged but I wonder if they did?
Considering that there were mages among Arlathan (as proven by Witch Hunt), it doesn't seem to have made much difference with Tevinter humans enslaving the elves in the first place. As for Shartan and his elven army, I wouldn't be surprised if mages comprised some of the men and women willing to topple the Imperium, but it's never been specified if that's the case. The story of Shartan's escape reads:
They say that Shartan's followers stole whatever they could find to make weapons. They fought with knives of sharpened stone and glass, and with bows made from broken barrels or firewood. This bow was ox horn, made in secret over the course of months by a slave who worked in the slaughterhouses of Minrathous.
The slave's name has been lost to history, and the verses that spoke of his deeds, stricken from the chant, but the weapon endures.
If you're curious about the kind of people who comprised the Long Walk to the Dales, here is an entry from World of Thedas from an unnamed elf to Brother Pekor of Ferelden:
Only sixty-five of our group made it to Halamshiral. Some gave up. Some sickened, especially the little ones. Bandits stalked us. My mother forgive me, I had to steal food. A child fought me for extra scraps of bread. A few days later, I carried her for miles after her legs gave out. She died shivering in my arms.
I used to have a master, a mage. He fed me well, never beat me, even taught me how to read so I could do his accounts. But if he had a theory or a spell he wanted to test out, he'd get out his daggers, have the other servants tie me to a post, and carve furrows into my skin. I was so afraid. Every time, I was sure I would die. But at worst I'd collapse, get bandaged up, and lie in bed too weak to move for days. The other slaves visited me in secret to survey the damage. I'd heal just enough before he needed blood again.
That is why I traveled from Val Dorma to the Dales with nothing but rags on my back. That is why there were one hundred and five of us when we set out, all elven. That is why I fell to my knees and wept when we crossed through the gates of my new home, a village for my people.
And now I'm reminded why I want to give the elves back the Dales, but that's off-topic. Let's move on.
You see I'm still trying to work out why the Dalish, and thus presumably the leadership in the Dales before them, have mages as their Keepers and you can only be a Keeper if you are a mage. Why would a people who had been suppressed and enslaved by mages, which would have included elven mages (if the rules in Ancient Tevinter were the same as today) have allowed it to become the norm that only mages could rule? Unless, of course, some senior elf mages, who had defected from Tevinter hierarchy because their race prevented their ascension to the rank of Magister, decided they would rather rule their own people. It would also explain why the focus of the new elven nation seemed to be the recovery of knowledge from an old elven empire in order to create a new one, rather than simply the establishment of the homeland that Shartan desired and why they pretty quickly dropped the religion that he had converted to.
Felicia Day said she was told there were Keepers who aren't mages, but I think the tendency towards choosing mages for Keepers has to do with how, according to the elves, everyone in Arlathan was a mage. To the Dalish, magic is a gift of the Creators. It isn't vilified simply because some people misuse it in the way that it is in the dogma of the Chantry of Andraste.
You're also looking at it from the wrong perspective: to the elves, humans enslaved them.
As for Shartan, there's a lot we don't actually know. I recall that some people even speculated that he had a romance with Andraste (given the impression some had about the play in "The Masked Empire" playing off a possible suspicion that this may have happened), but we know very little about whether he genuinely converted or not. Given how the elves continued to follow their pantheon of Creators, it doesn't seem any other elf followed her beliefs.
During the period between the end of the First Blight and the start of Andraste's Exalted March things were pretty chaotic with regard to worship, many people having lost faith in the old gods. It is not beyond the bounds of possibility that elf mages during this period, who were free to conduct research managed to turn up some old references to Arlathan in Tevinter archives and old elven ruins and took it from there. The ruins in Ferelden seemed to show that humans and elves had co-existed in the past and possibly even worshipped the same gods, but possibly under different names. I just can't see how the refugees of elven slaves would have recovered knowledge so quickly with regard to language and culture or preserved it during their years of slavery beyond anything more than a few folk tales. It does make sense if the source of knowledge was actually elf mages who had already been in a privileged position and then defected, with rather more lofty aspirations than the majority of refugees.
The developers mentioned the elven slaves wrote down some of their information on scraps of paper and the like, to pass down the information. It's also why Merrill points out there are gaps in their knowledge, such as why the Creators and the Forgotten Ones went to war.