Yes, a bunch of the Mesa 175s were bought by United... somewhat of a moot point now as Mesa is now a Republic subsidiary. It's a mechanism all the majors use - and allowed here by the UPA (section 1-C), as it makes it easier to move planes around to more favorable regional operators (least $$$) over time. (As an aside, way back when Air Wisconsin got booted by United in 2005-06, several CRJs were flying in USAir paint with registration certificates showing "United Airlines" as the owner. As long as the lease payments were made on time, I suppose everyone was happy...)

As far as buying a regional, there is language somewhere, I think it's a FA thing vs. something in the UPA, that prohibits the company from holding more than a minority stake in any regional carrier. As long as the WSCODs are around, I'd say Commuteair will be the operator. GoJet will be the exclusive CRJ-550 operator (unless SkyWest has some on line?)