US AP's can only be used with controllers set for US country code. They are locked to just US approved frequencies and power levels.
WW AP's can be used with any country code setting, including US. They are not locked to a fixed set of channels. So you should be able to use WW AP's in a system set for US country code.
But using WW AP's in the USA is forbidden by the FCC.
I hope this answers your question.