In Japanese version of the game he is a japanese student. Japanese version usually overwrights whatever Western translators put in the game. So as of now Soma is a japanese student.
And he is a reincarnation of the Dracula - that's why he had his abilities.
Wait, what?
Am I the only one who never seen the problem with this? In the Japanese game, he's Japanese. Konami, a Japanese game developer, made the reincarnation a Japanese teenager.... MIND BLOWN!!!
Seriously, if Americans made that story, I'm sure as hell to bet they'd make Soma American, just like Europeans would make him native to THEIR own countries.
As for Hector and Isaac, didn't Isaac believe the reason Dracula was defeated was because they weren't there to "protect" him? He blames Hector from as a turncoat, for abandoning the Master. Not to mention, both Hector and Isaac's powers were drawn from Dracula's(one of the reasons why Dracula needed one of them as his vessel to be revived in CoD). Of course, what Isaac thinks is beyond the actual point. Didn't Zead/Death lead him on, use him just to bring Hector(the suitable host) back? I can see a battle in a remake of CV3 where you fight Hector, then after you defeat him, there's the whole, "Wait a minute... this isn't right" type of speech where Hector realizes he shouldn't be fighting Trevor and crew because of what Dracula's doing. Then Trevor letting Hector leave, as Hector gives Trevor and crew his blessing to put an end to the Dark Lord. Then later, you encounter Isaac, who's searching for "the coward" Hector, you battle him, but the battle ends with his escape.