In principle there is (almost) no architecture specific code in sys-kernel/dkms, so things should just work on all(?) architectures. Note that the upstream test script fiddles with /lib/modules/$(uname -r) and for that reason it does not really work in the sandbox. Nonetheless, you can run the test phase in some (docker) container (this is what upstream does) and override the test restriction with ALLOW_TEST=all and FEATURES="-sandbox". A kernel with module signing and compression support is required to run all tests successfully.
