Check the laws in your state. Many don't require you to have workers comp if you are under a certain number of employees. In IL and TN that number is 5.
But, you are taking a risk. Occ Acc., while I believe is better for an O/O than workers comp, doesn't protect the employeer (you) when the driver gets hurt.
But the cost is much higher for an unrated company for workers comp so it may be worth the risk if you set yourself up properly. But IL was 29% and 23% in TN. OUCH!
We have set-up a program for small fleet owners that will allow them to be legal. We call it the two pay system. The driver works for us and is under our pay system, safety, work comp, insurance, etc. And then we pay the fleet owner seperatly. Not likely the perfect system but keeps owner legal and takes all the head aches out of compliance side of business.
We have done that for a long time. Keeps you covered if there is a problem and the fleet owner get a large break on UMC and comp compared to being in a pool. Also get the drivers access to reasonable(matter of opinion)medical insurance. Even have some O/O's that incorporated just for the medical.