Guys, when have Varric ever seemed to care about dwarven traditions? I don't think that he'll use that as a gating excuse.
He doesn't.
Born on the surface, Varric has little love for his underground brethren
(character bio on website)
In addition to what he said in DA2 to begin with, his bio makes a point that he doesn't really like the Orzammar dwarves very much. All of his contacts are Merchant Guild.
I can't really imagine the Merchant Guild caring about whether Varric has a child or who he's dating.
I think it's more likely that the reasons he would have for not dating x race would be: He's just not into them. In the case of Qunari, he could also be uncomfortable being with a qunari because of the bad memories from Kirkwall.