In my understanding Microsoft does not state explicit requirements in the MPA Partners sign when enrolling as GCC CSP Partner - at least I could not find anything in this regard in a copy of the MPA I have (Please let your legal/Compliance team check the agreement that is eventually presented to you when you apply).
There are certainly requirements, but those are defined by the government agencies themselves, in the applicable compliance standards and regulations - like ITAR, CJIS policies etc.. In other words, for your support staff you need determine yourself how to fulfill the requirements of those governments and applicable regulations for support personel. E.g. Microsoft does assurance screened staff running the cloud environment, but does not state that support agents are located in US:
https://learn.microsoft.com/en-us/office365/servicedescriptions/office-365-platform-service-description/office-365-us-government/gcc#office-365-government-gcc-environment-screened-personnel
https://learn.microsoft.com/en-us/office365/servicedescriptions/office-365-platform-service-description/office-365-us-government/gcc#office-365-government-gcc-customer-support
Office 365 GCC customer support is provided under the same terms and conditions offered to Worldwide versions of Office 365, including no support agent physical location or citizenship assurances
