Well, let's face it- that kind of stuff can happen in any line of work, especially labor. I don't think it's any more prevalent in the San Diego hull cleaning community than anywhere else.
As far as your other question goes, absolutely, you can start your own hull cleaning business without any prior experience. But I look at your working for somebody else sort of like taking skiing lessons. Sure, you could probably figure out how to do it on your own, but taking lessons shortens and flattens the otherwise very steep learning curve considerably. I'm assuming you have no previous boat maintenance experience, yes? Going into this business with zero knowlege about the systems you will be asked to maintain could be potentially damaging to your client's boats and harmful to your professional reputation.
If it's me, I'd look at working for a reputable dive service for as long as necessary for me to feel comfortable picking up my own clients and answering their questions about hull cleaning.