“ I have several friends with their own airplanes that I could fly in, but I'm not sure the airlines would view GA piston time as anything useful. Any inputs on this?”
GA piston time is all that the majority of your indoc class will have at the regionals, excepting a handful with Cessna 208 time. If you can get PIC time cheaply, either with your friends or at the aero club, do it. But the key thing is to get the instrument refresher, and no, not a FAA check ride.
https://www.law.cornell.edu/cfr/text/14/61.57