So, according to Trafton, rating N/A reviews is perfectly fine. ;p Whether you see the review as a comment and not a real review is a different matter. If, however, someones writes a review tha doesn't fit into J2o's rules and gets edited to N/A, then you should still be able to rate it. IMO the rating is for the author of the review, telling him how good he has done and not for the author of the upload, telling him how good the reviews of his upload is. The review rating system is supposedly supposed to discourage bad reviewers, or at least encourage them to put in more effort.

EDIT: Don't forget that some ppl may rate a review with a rating only to find that the admins have taken the rating away and set it to N/A. Now, if you follow the winner, what are you going to do? There's no way to take away the helpful/unhelpful rating you gave and you have also, all of a sudden, begun to annoy ppl because they think you have rated an N/A review.