They have an exemption to work with other organisations that use Huawei. Often, Huawei are the only vendors for telecommunications equipment in the area.I also remember reading the US military has a waiver from Congress to use Huawei gear on the basis that it is important for national security. Why? My guess is because it's more secure (hack resistant maybe?) and reliable than Cisco. I wonder if it's also possible they use it for 4G and 5G instead of Nokia/Ericsson.
IIRC they don't actually use Huawei devices themselves.