JetBlue pilots, yes. OAL pilots, not in the flight deck jumpseat unless it's to a US territory. I would assume that means you could jumpseat and sit in an empty cabin seat, just not a jumpseat.

As for checking loads, if you're not a jetBlue crewmember, best way to check loads is to get someone here to do it for you. You can call the listing number, and they'll sometimes tell you the loads.