Raspberry Pi products can be found in a lot of industrial/professional setups, especially things like their compute module range(s) that can be dropped into off-the-shelf, or custom carrier boards. Others can be a bit more hit and miss, though Libre Computer are up there with great software support, and will have their own compute modules available soon.

Most professional high-volume projects wouldn't use Raspberry Pi as it is, because those boards contain functions they don't need. So they would design their own board which will be cheaper and more compact by including only functions they need.

That's why there's "Compute Module" SoM with minimal functionality. It is made for professional designs.

But if you want to produce low volume product or you're 100% fulfilled with Raspberry Pi, there's nothing "unprofessional" about it. PCB is PCB.