Even girls like the maid Tutu and Carla, who are humanoid monsters, are considered part of the subhuman race. This is because, although their mothers are aliens, their fathers are human. So, under the standards of the Tribunal, they belong to the subhuman race rather than the alien race.
Furthermore, from the perspective of the Tribunal, the Beast Race on the War Planet is also considered a subhuman race, given that they are derivations of humans.
Therefore, the standards of the Tribunal for judging the subhuman race are quite clear: not only should you resemble a human, but your ancestors must at least be humans. Races like the Ashali People, who share no relation to humans eight generations back, are considered aliens no matter how human they look.
If applying this to Regnes, the orthodox Dragon Race would certainly be aliens, while those born of a mix between dragon and human, the Dragonkin, are subhuman.