In addition, the tone is much more sombre. It's not something that couldn't be overridden by the group, of course, but there's little to Buffyverse that's specific to it except for the tone.Yes, mechanically. There are no hard restrictions on the various supernatural types so it’s easy to build a power set however you like.
Settingwise, there are no slayers per se. There are hunters and bodyguards with supernatural abilities, most via a pan-religious organisation.
I mean, being a Slayer could just be considered a two-point trait and that's about it. (Or maybe three or four. Point being, adding slayers wouldn't exactly be hard.) You'd have to ignore or re-interpret most of the setting material in the book, though, due to tonal differences.