Update: got it working with the IOGear USB sharing hub after all. Not sure what the issue was, or exactly what fixed it. I think it had something to do with removing the cutter from the list in Sure Cuts A Lot 4, then putting it back in.
My business' main work isn't working with vinyl. We got it mainly to do our own signage around the shop, and do occasional jobs for customers that specifically request it, so investing in a nicer cutter isn't worthwhile. The cutter is only 20-25ft away, so it's not going unattended. I just got tired of having to wheel it out and plug it in via USB directly every time I wanted to use it.