There's no limit on visa exempt entries either. You don't need a visa if you are in for less than 30 days and out for say, 30 days. You are a tourist. I have a friend who came every other month for years with no problem.
But that said he should have no problem coming in and out on visa exempt stamps as long as he can prove he works OS and has income from work outside Thailand. He should carry pay slips and proof of job with him when he enters. I had an oil worker friend from Alaska who worked 30 days on/off and visited every second month for years with no problem.