as a beginner, i do not think i could often tell by looking if someone in a hakama is doing 'good' or 'bad' Aikido. i do think i can often tell if they are doing what was shown to us or something different (according to my perception, at least). i think i can feel (not usually looking at other pairs when training, anyway) what they are doing to me, and can sometimes translate that into whether it would work for me (my size vs theirs) or not, and sometimes actually reproduce it...but don't know if i have much to judge the skill level---to me, if it works for me, it's good. and a lot of the time, i feel it but just can't convince my body to do the same
as for rolls, i have seen 3rd kyu and above who have terrible looking rolls, perhaps for a variety of reasons (health, fear, laziness, who knows or cares)---just another reason not to use the hakama as an indicator of ukemi skill any more than technical skill. Assume the best of that 'unknown quantity' of a partner---they may surprise you.