I've been running a Jesel belt drive for years and never had any problems with it. The only problems I've ever seen are rocks or mud getting in the belt and taking the belt off. When that happens it's major damage to the valve train and usually the heads and pistons too.
That's not much of a problem for guys that are on the road, but I would never run a belt drive without a cover. Jesel makes covers for small blocks, but not for big blocks. However, my motor builder has made some really nice billet covers for big block Chevy's.