"Released in Japan in 1997, Vampire Savior 2 (ヴァンパイア セイヴァー 2, Vanpaia Seviā) was released along side Vampire Hunter 2 and uses the same gameplay mechanics as Vampire Savior. The game adds Night Warriors: Darkstalkers' Revenge characters Donovan Baine, Huitzil (Phobos in Japan) and Pyron to the Vampire Savior cast while omitting Jon Talbain (Gallon), Rikuo (Aulbath), and Sasquatch.
Although the game was never official released in arcades outside of Japan, the game was incorporated into Darkstalkers 3 (Vampire Savior) and later as it's own standard game in the Japanese only release of Vampire: Darkstalkers Collection." - Darkstalkers Wiki
As far as gameplay differences, besides the character selection, VS2 has every character vs Jedah and one ending.
It's not really a replacement for VS, its like a different flavor, along with VH2.