Yes, but you don't have to meet Viconia, or have her in the party.
Plus, one can always use Jordan's excuse for everything. Yep. You've heard me right. Charname is a ta'veren. Sarevok is a ta'veren. Heck, all Bhaal's brood are ta'verens! That explains it all! Fate Spirit is really a loom of Ages, that spins the Pattern of the Sword Coast's history. And it weaves as it wills. So, if it wants to weave a planewalker into the Pattern, who are we to say no.
I dunno, I really like giz myself, and if we can't play with them in a game set in PS setting - which is not possible - I'd gladly add one onto my party in BG1. I think that Eranon's excuse to be on the Sword Coast is better than Viconia's or Xan's, or for that matter Drizzt's and Elminster's, so...