I have offered my little guys a basking spot the entire time. In 4 months ive seen 1 on it and it didnt look like he was up there for long. I beleive they do just fine in a fully aquatic enviornment.
CSX had one(possibly 2?) in fully aquatic with pbass/cichlids/etc. It's arguable to no end whether it's right or wrong. But from what I've seen should do fine with no basking spot.