What do you think would happen if Soma killed a vampire and absorbed its soul? I personally think that it may cause Soma to revert into Dracula. Think about it, in Dawn of Sorrow, when Celia kills the doppleganer of Mina, his anger of thinking Mina is dead causes him to summon the chaotic power. However, Arikado(Alucard) calms down Soma and tells him that it was only a doppleganner(spelling) of Mina. It is at that point that Dimitri leaves Soma's body with the little chaotic power Soma summoned and uses the doppleganer(spelling) as his new body. At that point, Dimitri says that while Soma was starting to transform, he was able to scan the memories of Soma's past life. That seems to be evidence that if Soma turns evil and gains the chaotic power, he would have his memories from when he was Dracula. So while Soma's body wouldn't change much, he would be Dracula mentally.