Jake is not Steve (as he died during CV and the spiel about him coming back was nothing more than a jab at Claire) besides Steve already had father who had already mutated into a T-Veronica zombie//mutant and was killed wail doing his only epic moment in CV
So in short Jake is a new character that was created from nothing more than a fling during Albert Wesker's early years.
It probably was just a 'jab' at Claire as you say, but even if Steve had no hope in being "reborn", he still has a striking resemblence to Jake.. Also, there was a character in Resident Evil: Outbreak, by the name of Greg Muller, (The same pronounciation and spelling as Jake Muller) who was a head researcher for Umbrella, that was known for developing a 'technique' to induce partial or specific amnesia.. As we know of, there were two patients (Yoko Suzuki and Alyssa Ashcroft) who recieved some treatment with the amnesia in 1993, so it's clear that he had been using the technique for a while.. Although Greg was later assassinated, it doesn't cross out the possibility for someone else to have picked up on his research afterwards, right..? (Wesker perhaps?
) I'm thinking that Steve was reborn to be this, 'Wesker Junior' (with all memories of his past wiped away, and new ones to replace them, like that he was the son of Wesker, etc.) ...
I think this makes more sense, because of how much they look alike, (Jake and Steve), plus, that Wesker took Steve, (& HINTED that he could return!) ... Maybe he intended for Steve to continue with his plans of 'Complete Global Saturation'? :O Anyways, I personally think this (If it's true) would make up to be a great twist in the storyline for upcoming Resident Evil games, rather than for the great Albert Wesker, to have a real son. (Who looks somewhat to nothing like him, and came out of nowhere..) :3