I was honoured to be a guest instructor at the local Shito-ryu gasshku this past weekend. Just prior to my session I was watching these fine karate folks doing some tanken dori. Very, very similar to aikido although, as one might imagine, more strikes and rougher take downs. I noticed a basic arm bar and shihonage as two techniques that really stuck out as similar. Also, their irimi was significantly more shallow than how I have been taught...but it was there. I'm glad I went early as it gave me a theme to work with...irimi.
I remember doing similar techniques back in the day now doing Aikido brings the memories back even more, however one point to your observations whilst the take downs may have looked rougher I dont think they where as Karate students you learn no form of ukemi what so ever or at least we never did so every take down seemed rough as none of us knew how to fall.