Bare earth, or gassy soil, coccidoses can still become an issue any place rabbits have contact with their own feces.
But, it's mostly a problem in humid areas.
I have a friend in CO that keeps her buns in a big outdoor colony, and says she's never seen cocci.
Here in PA, I had mine outside for most of a year with no issue. I placed one infected rabbit in there prior to butcher, but I let the pen sit empty for a month afterwards, so I thought it would be OK.
It must have been a particularly nasty strain, because what happened to the kits was brutal.
This is what livers looked like after two weeks exposure.
The siblings of those kits who had been kept in wire cages were fine.
So, I don't dare keep my buns on dirt(or grass) here, but other people sometimes can.
If you are nervous about the pen, feeding your buns more grass hay and less pellets can help trim them down, reduce your feed bill, and increase their likelihood of successful breeding.