HK CAD recognizes the US ATP. We didn't have to take any more writtens than the other guys. You might get a break on some of them if you had UK license, but that would be because the rules were based on UK rules, not some secret plot against Americans.
I never noticed or have experienced any problems with having a US background, nor have any of the other guys I knew.
As far as differences in the interviews, consider that someone who has already migrated from one continent to another may understand better the realities of moving somewhere a long way from home. Or at least have a better idea of the concept than a fella who has never left Cleveland. So, there may be some different questions asked of the two candidates.