Well, in this I see a reminder that ukemi is there for a reason... admitedly, a beginner (even a 3rd dan karate beginner) may not know much ukemi, but he should know two things: to tap, and that resistence increases risk of injury--- or some dojo is not teaching its beginners basic self protection. Most serious injuries I've seen have come from uke resisting (through fear occasionally, usually through inflated ego) past the point of stupidity, coupled with a nage with limited ability or equal ego issues, and either large size or good skills.
There are chances for really big nages to injure little ukes anyway (the only thing I usually can't get ahead of in my ukemi is a tall strong nage who literally lifts me up off my feet, not too bad in say irimi nage, but hard on my shoulder in shihonage). But I am not adverse to tapping if they put me in a situation that can hurt me before I can get ahead of them (and if they don't notice the tap I usually kick them
). But I doubt there was that much size difference between those two sandans. Something tells me there was more than Aikido (or a lack of Aikido) going on there.