Yes, Google is the only one championing NaCl right now. I don't see how they get from their current position to some sort of lock in ala Microsoft though.
What does NaCL have to do with Google APIs? It's a client side technology. You can talk to whatever server(s) you want. (Presumably subject to same origin policy like JS, which if anything means it's easier to talk to your servers rather than Google's or someone else's).
