I can't tell you what he was like as a kid before Spencer picked him up. Not sure if that's even been unravelled lore-wise.

I actually believe that, yeah, even with him carrying the Progenitor Virus. Wesker was reconditioned, groomed and abused as a kid, and turned into something he wasn't. I probably wouldn't have given up hope (if he'd let me get close to him in a what-if scenario) of getting through to him, even if I'd had to sacrifice a lot myself for it.