You can find footage on the net..... I found 9 pre ww2 movies (searched "aikido mpg" on google...) Also, theres two on aikidofaq.com.
Anyhow, I've seen what looks like what you describe, and I've seen people who certainly didn't throw themself. I read about (? guy who started yoshinkan?) a judoka who decided the uke WERE throwing themselves who took on O Sensei. I believe he was flying through the air when he realised that they were in fact thrown.
Must be said that anybody taking Ukemi from O Sensei who threw themselves would be in trouble, though. Ukemi isn't about guessing where he's throwing you (which can cause nasty injuries when you're wrong) but letting your body follow softly and be thrown. This would only apply more forcibly in the case of a master endowed with such subtlety in his technique. If you're going to jump first, you might as well struggle maniaclly and take the atemi. It's just as close to good Ukemi.