If it has locked up then it's probably all beat to hell and yes, it could let oil pressure bleed through the bypass circuit. Take the plug/spring out and inspect it. I think it's a good place to start.
I know you don't want to hear it but - put a gauge on it. See what the idle pressure is. For your sake I hope it's above 10 psi.
Dude, I really wish I could be there to help you.