So, it is not:
http://www.airservcorp.com/who_we_are.php handling the luggage at the United terminal at O'Hare?
I am also starting to wonder where the issue really is in the delay. It seems that many times the plane is unloaded rather quickly. I started seeing folks unloading while I was still in the plane (front rows). I think UA will do a reasonable job to transfer luggage to connecting flights which would require quick tarmac operations. I am wondering if the letdown is simply within the terminal for moving the carts to the belts and unloading....
Actually it looks like ASIG has "ramp handler" jobs, but maybe not for UA:
http://www.asig.com/job-search/?lang.../jobsearch.ftl
I found this job which indicates UA as the employer:
https://chk.tbe.taleo.net/chk05/ats/...&source=Indeed