mtlogcabine - Yes, the product I'm talking about is Vbuck or similar vinyl buck. Vbuck and a couple of ICF block users have told me they've never had the code issue raised, but no one could give me a good reason why either way.
northstar - thanks for the link to ES Report 1911. The ICF manufacturer, BuildBlock, said their postion was that a vinyl buck could be considered a subassembly of a vinyl window, and code doesn't say you can't use vinyl windows.
all - Yes, understood that discussing with AHJ is crucial.
Thanks