You should consult your county's building inspection department, because while most older sunken dugouts don't have them, my guess is that any newly constructed sunken dugouts will have to have ADA ramps. The government will want the dugouts to be handicapped accessible. Who knows, someday your team manager may be wheelchair bound.
You will also need some sort of under drain system, unless you like standing water.
Personally, I don't think they're worth the trouble.