That horse is long gone. In fact, it's not even the same horse through the whole set of stories. Geralt just names every horse he has "Roach".roach (not vernon but the horse from the last wish, a portable innkeeper for gear)
I checked the IMDB for Witcher 3, and apparently they have hired a voice actor forDudu Biberveldt
Well, you get to see Vetala later if you let him live. In any case, I think the whole "WTF?" factor was the whole idea. He wasn't supposed to be explained. He's just a friendly ghoul tryin' to get by in a cold, cold world.That talking Graveir. Such a "huh?" moment and then a complete lack of followup.