Basically, I've never used hard wets in GP4 during my time in league racing. The thing is that the soft wets provide a lot more grip (due to softer rubber) which is an even bigger advantage in the wet. You have to be careful though as they are worn really quickly especially when there's less water on the track. The harder compound provides less grip but lasts for a longer distance.
I'm actually not quite sure about the CC cars but I presume, their tyre choice depends on the strategy data (which is defined in the magic data of the track). So they're determined randomally all over the CC field, also in the wet.
So as a conclusion: I've always left out the harder tyres in GP4 as the soft tyres providing a lot more grip easily make up the fact, they're wearing more quickly.
regards
chris