If he was an ASTAR pilot, the indisputable fact is that he IS flying DHL airplanes, freight, schedules, and using DHL a call sign. As a legal matter, it may be ASTAR that's signing his paychecks, but he's working for DHL, plain and simple.
Obviously, the same applies to our brothers at ABX. We're ALL working for "Da Man."
As for the legal situation, there may be some hope on the distant horizon. The NLRB recently ruled against FedEx and their use of so-called "independent truckers" in their ground-haul operations. There are some clear parallels between those operations and DHL's use of "independent airlines" in transporting freight. Obviously, we're still operating in a very gray area here. We're "employees" when it suits them, "independent contractors" when it doesn't. DHL is doing a very effective job of exploiting the void between the rules regarding foreign ownership of domestic airlines and established labor law. We need to be equally effective in seeking interpretations of those laws in our favor.
These are just a few of the things that the pilots of both groups should be highly concerned with. Who signs your jumpseaters paycheck or the logo on his tie tack needn't be one of them.