Dear Wonder Warthog,
I believe that it isn't unusual for non-Catholic clergy, including Episcopalians and Anglicans, to go through a brief period of seminary training, although I don't know if it's required of every candidate.
sitetest
I suspect it is decided on a case-by-case basis. But the place to find out "is" the Coming Home Network. I've read a number of the conversion stories of former Episcopalian (and now Catholic) priests there and in the "Suprised by Truth" books, and I don't recall any mention of additional seminary training in those--but that hardly constitutes a statistically valid sample.