His liability policy would cover any damage he might accidentally do, but it won't cover him if he is hurt. In most states, you cannot be held responsible if he hurts himself. You might want to check your local statutes.
If he has a liability policy and can provide you with a dec page or certificate of insurance, I think that speaks to him being a professional and protecting his clients. Individual workers comp can be outrageously expensive- more so than taking the risk of having a couple of minor injuries he would have to cover himself. That is his choice, in my opinion. Ask for a cert. of insurance and references, and if you like his work- I say go for it. If he is known and established, I favor giving my business to the guy who is working hard to get by.