The ToH and OA yetis are different. Can't say how as I don't own OA. But ToH... now that is a MONSTER book. I would recommend it to anyone. Tons of oldy goodness. Some have mentioned it's sometimes low-quality artwork, but I bought it primarily for the stats. ToH is a book I think most DM will find they use over and over, maybe (for me, at least) more than the MM.
GO BUY ToH!!