Yes, the master unleashed AP is acting as a Zone Director and it sets the country code for all AP's under it's control.
Having the controller set to US code will keep you in conformance, using only FCC approved channels and power levels, if you are using the ww AP in the USA but because that AP has the capacity to be set to another country you are technically using an AP not approved for use in USA. Authorized resellers should not sell WW AP's into the US market.
If you are buying on the Internet from non-authorized resellers or as a second hand AP then the AP technically has no warranty with Ruckus.
But, it should work!