Unlike IFComp, there are no rules that prevent you rating a game that you play tested. So, go for it. I will certainly be rating the games I play tested, but only after I've played the final versions. I'm leaving that until I've played all the other games that I didn't play test.
It's quite nice to know this is okay--I confess I'm worried I'll be biased more towards the games I beta-tested, because I understand their workings more, and I more totally understand what the authors wanted to do.
That's my current stance, though I may rethink it. Not that I want rethinking it to get in the way of finishing all the games I can.