On the subject of Ukemi-Waza on hard floors: I spent many a session as a yonkyu/sankyu wishing we were practicing Mae and Ushiro-ukemi on a lovely soft floor. Then I went for work experience during the summer to Brisbane, and trained with the club there.
Their Dojo was carpeted, and some ukemi I saw were quite bad - I saw one guy about my grade (sankyu) kneeling down, rolling horizontally across his back, get back up. Since then I have cut down on my complaining about ukemi on hardwood floor(not completely, though... ).
On Aikido ukemi: I attended an Aikido session last year, just to see what it was like, and found their ukemi to be virtually identical to ours. Of course, maybe I was just doing them wrong