Pros, whether regional or touring, have to bowl somewhere when they are not competing full time. There have been local tournaments I have bowled where PBA regional guys have entered. They do not always win the whole thing. Heck, they have even entered no tap handicap tournaments and not cashed.
The USBC makes it clear that employees can bowl, but can't cash. Seems like a fair deal. It all boils down to accepting that professionals might be bowling and taking the chance, or just walking away and not entering. Bowling is a sport where winning is not a sure thing. Anyone has a chance to beat anyone else at any time.