If they are hired through normal hiring portals, listing the party membership status is a standard feature of said portals, so yes it would have been known. If

If they are hired through normal hiring portals, listing the party membership status is a standard feature of said portals, so yes it would have been known. If they hire directly, they probably asked and may have been lied to. I highly doubt that Chinese tradecraft is so bad as to compromise purposefully and successfully planted undercover agents on assignment with foreign nation-states or similar by listing them as party members in low security databases... but you never know! Bureaucracies being what they are...