In some senses, not all.
They can still see where they are going and each other, so the danger is down to their ability to ride in the wet. That's manageable and makes sense to let them race.
In F1 the danger arises because they can't see a bloody thing, so it's not about their skill, it's just sheer dumb luck and hoping there's nothing stopped or slow in the wall of spray you can't see through. That's not something you can overcome with skill, you're just putting people at a pointless risk that they have minimal control over.