Sounds like everybody is in agreement here. Non Rev = no check in. Physical jumpseat = obvious check in.

As long as we're here, an annoyance is when some dude interrupts us reading the checklist and says, "I'm on the jumpseat". Amazing how many times this happens.
I'm not old and bitter yet, and I'm not on a power trip, but isn't it just as easy to ask, "Hey - I'm trying to get to work. Can I use the jumpseat?"