I think that is the key...
If one wants to use any flight instruction carried out towards the IMCr for the FAA IR then to be safe they should use a JAA FI who holds an IR and is authorised to teach the JAA IR (or only count that time towards the FI time) - so in otherwords if you used a JAA IRI then the FAA would not complain - I have no doubt about this.
What TH is complaining about is people who have done their training with a NON-IR'd non IRI JAA instructor. I can see his point that the FAA may complain about this - the instructor was not authorised to teach for an IR.
However to say that "IMC time doesn't count" is simply wrong because any time spent under the hood counts towards the total instrument time, it may not count towards the "Instructor time" but that is a different matter.
Realistically most people going to the USA will need 15 hrs or so with an FAA CFII to get up to scratch and meet the other requirements (like cross country flight "under ATC controlled routing")......