The reason for the US flight (should that be flight?) suits was because we were renting the aircraft. Under the contract they had to be operated in the same way as any USAF ac and that included flying suits and head sets. Not sure what the excuse is now though - maybe we really don't want to lift that stone!!
If I recall correctly, after a Hercules operational accident one of the aircrew was delayed in evacuating from the wreckage because his CS95 caught on something? There were no DPM flying suits available back then, so use of CS95 had been approved - but no-one had done a compatibility assessment.
If US flight suits have been fully assessed for compatibility with the C-17, what would be gained by spending a lot of time and effort, not to mention money, on re-assessing UK flying suits / AEA for use in the aircraft?