Oh, of course LOL. But they would have no reason for it. Judging one category and being judged in another have nothing to do with each other. If someone's going to be biased on their judging, they'd be biased whether their friend was another judge or not. But hopefully the rubric cuts down on that as much as possible.
As far as the rubric goes, maybe this year there could be a place where you have to add just one line that explains why you gave the score you did for each category... either that or a place at the end for a general comment about the story. For example, if you give a story a 3 out of 5 for grammar, you could write something like, "The story was readable, but there were a lot of incorrectly-punctuated run-on sentences that really took away from the flow, along with other typos and errors." Then if the author requested to see the score sheet later on and was like, "What!? My grammar is impeccable! Why did I only get a 3?" they would know. As someone who judged last year, I don't think it would be asking too much of the judges... it would basically just be putting into words what should already be going through your head anyway.