Anyone who can paint DuPont's Imron can paint any other polyurethane paint. It's the same as the difference between choosing Sherwin Williams versus Glidden versus Dutch Boy for your house -- it's more a matter of the type of paint than the brand name. You buy one latex with an all-acrylic binder, it's pretty much the same as another latex with an all-acrylic binder, all other things being equal (% solids, pigment material, etc.).
The only real issue is which paint supplier your shop works with, because that's where they'll get the best deal on price based on quantity buys and exclusivity. That's why if I get my plane painted at Reese, it's going to be Jet/Acry Glo -- because that's what Ken buys. I'm sure if I wanted, he'd use Imron, but the cost would be higher and the result would not be different. If I take it to your shop, I get a DuPont paint, because that's who they work with. The key is getting the right type of paint, i.e., a high-quality polyurethane rather than a cheap enamel.