That really passed my attention and I don't think anybody has mentioned it yet. But you're right.
I am guessing that the tattoos were reserved for a select few amongst the Dalish, maybe reserved for clergy? Those in political power like Ameridan?
I was more thinking it was an oversight when the character was made, but sure, it could be that. 
And yes, as I've understood the lore, the Dalish started with the tattoos to gain some of their culture back -- after they lost their second homeland of the Dales. Which Ameridan was not there for, as he was locked away in stasis. He had no idea the Dales had fallen when you wake him up.