It's got to be the same book. Perhaps with a new formatting or preface. Same author, same title.
The ISBN doesn't matter, observe these 2 editions of Hitchiker's Guide to the Galaxy, both paperback, with 2 different ISBN's:
http://www.amazon.com/exec/obidos/tg/de ... ce&s=books
http://www.amazon.com/exec/obidos/tg/de ... ce&s=books
The Ravenloft Covenant thing is probably one of two things:
1) An attempt to woo Laurell K. Hamilton fans into buying it by attaching a word often linked to Vampires and fool them into thinking it's another of her vampire novels. (I haven't read them, so I don't know if she uses that term or not.)
2) (unlikely, but we can hope...) A start of a new line of Ravenloft novels and/or reprints.
Either way, it shouldn't have anything to do with the change in license, since the WW license never covered novels, WotC could have done this at any time they wanted.
"We're realistic heroes. We're not here to save the world, just nudge the world into a better place."