Their systems are separate, they have their own dispatchers. The only systems that may be shared (besides ticketing/passenger related ofc) are gating and ramp tower. At ORD, mainline runs the ramp tower (calling for push and start) and gating for mainline, Envoy handles gating for all regionals.
even with all of that, if inbounds were held up you would think the agents here in the club would have known something. I went up 3 times with 20 minutes between each time to see if they knew more than what I could find and nothing.