Seems like roman-like gladiator fights had to be reinvented to meet your benchmark for "objectivity". The question is, would you prefer to stand in the arena or to watch this experiment?
Please give e definition of an "uncooperative opponent"? Someone who wants to kill; someone who wants to fight by all means; someone who's running away; someone with a hestitant attack?
Taking ukemi from someone is in my opinion a very usefull method to judge about ability or technical features. In fact my exprience in taking ukemi is the central aspect where I can judge if there is a congruence between what I am told and what the practise is like.
The analysis of videotapes etc. can be compared to scientific methodology in social science. Why should this not be a proper way to gain insight? Especially when there's the possibility to do the comparison with subjektive impressions of ukemi?
Especially when there is not other way left over?