Yeah, VS is definitely set in teh same world as FFT, I know that for a fact. For example, FFT is narrated by one A. J. Durai, son of one of the main characters; a "quote" of his is featured in the intro of VS, and a lot of items refer back to FFT's main characters, e.g. Agrias, Cid, and several others. A lot of people would claim this to be just coincidence, but go read their descriptions and you'll see what I mean =P

EDIT: Found THIS article on FF:WA about the FF6 Prequel =D?