Not even skywest pilots can list for jumpseat ahead of time for their own flights. There's no way to do that on the united system although I think mainline pilots can. We have to just go up to the gate for any United or United express flight and ask.
As far as checking a bag when jumpseating I've never tried it myself but I've asked other people about it and everyone has told me it's not a big deal. Go up to the ticket agent with your badge and tell them what flight you're going to be jumpseating on and they should let you check the bag. Whether or not they try to make you pay may depend on the agent.