Actually, I read a study in the past(it might of been in one of the old-old-old paper versions of Aikido Journal, not remembering now.) but it actually said shihonage had the worse track record for injuries. Iriminage was also really bad. But techniques like koshi and jujinage were relatively low for injuries.(I'd like to point out that they included university clubs in the study. They attributed injuries at these clubs to poor instruction, and a lack of high ranking students to administer classes...so basically a bunch of 19 year old guys messing around and accidentally hurting each other.)
O'Sensei killed one student and seriously injured another in the same seminar. All the deaths I know of are from the original honbu dojo. I think at least two or three were from shihonage. The most serious injury I've seen in my organization was caused by hakama entanglement (totally jacked up his leg, torn something or other)...although I am quite cognizant of the high injury level in aikido. Even though 99% of aikido is cooperative these injuries still occur, usually due to a lack of control on the part of nage b/c they halfway learned technique, to include ukemi. See how I brought that back to ukemi? Full circle, baby, oh yea!