I have almost all of the Kult products - even the rare 2nd ed of the game. There is definitely overlap (which is what got me interested), but the creatures are not "the same" by any stretch.
Let me know if there are some specifics you want.....I'll haul the books out and take a look.
As far as the game itself, it was very very VERY dark. That said, I enjoyed it every time I played. I never actually ran this one...just incorporated some of it's ideas into my Mutant Chronicles game since I ran that with a "Lovecraft meets the X-Files" sort of flavor.