Terry Ezra, to my knowledge, has been involved with aikido since the early sixties. I don't know who his first teacher was, but his paths crossed with those of Chiba Sensei pretty early on in the history of Aikikai of Great Britain (later the British Aikido Federation). I would guess he had quite a few influences along the way, but mainly from the Aikikai side.
I have always had a feeling when I practised with and watched Terry that he admired Tohei Sensei (though he might contradict me!), which might explain your perception of a link with Seidokan, but I would be very surprised indeed if there were any formal link.
Actually I don't think his aikido has much similarity to that of either Chiba Sensei or Kanetsuka Sensei, which is perhaps surprising, given his long-term contact with those two teachers.
I concur with you last sentence in you blog.I saw little if any of similarity between Chiba Sensei /Kanetsuka Sensei. I saw him at the first J.A. C. course and in Cardiff.Did not get a chance to practice with him , so I do not know how he moves etc.As you know he took ukemi from Yamaguchi Sensei , so maybe this is where is interest /influences came from? Cheers, Joe.