Support for generating keys from known DH parameters is not included unfortunately because even the latest stable GnuTLS release doesn't have the necessary support. I have a patch that implements it using _gnutls_dh_generate_key() but that requires a special GnuTLS 3.8.2 build (--enable-fips140-mode). With that patch all included tests pass here.
Paul, can you take a look? I included your tests so please approve this MR if you think it's okay.