pikeyton --
I'm sorry if my lengthy response did not explicitly answer your question. I did however believe that one could have easily seen that nugget of information you seek....
Again, these combined programs are designed only for those hard-core future academicians planning to pursue a life of research. From many comments I've read over the months on this board, it is clear that many (most?) people heading into radiology do so for the big $$$, 2-3 months vacation each year, short days, etc.
As none of the above describe the life of one who would leave one of the combined programs, it seems clear that only a relatively small percentage of those into radiology would seriously consider a lengthy 7-year track like this. Therefore, the relative competitiveness should be decreased, though the absolute competitiveness due to 5-6 total slots remains high.
As for the IMG issue, any hypercompetitive environment means a harder track for IMGs. However, many IMGs I know have considerable research experience. I seriously doubt anyone (US or IMG) would stand much of a chance in nabbing a slot in one of the three combined programs without an impressive research background.
So, while all this could have been inferred from my previous post, I hope making this explicit helps you out a bit more.