Sebaceanoid refers to any unnamed notable genetic variant or subspecies on the Sebacean physiological type. This is to say, any species that might have the initial appearances of a Sebacean, but upon closer examination bears remarkable differences.
Such examples are the Sykarans, seen in Season 1 in the episode, (1.6 "Thank God It's Friday... Again"). Aeryn Sun referred to the species as "a distant cousin, at best." Other examples are members of the Clansmen on the Royal cemetery planet. They would appear to be Sebacean in all respects... except that during pregnancy the distended female abdomen becomes translucent, allowing the developing fetus to be seen within. Until Aeryn Sun became pregnant with D'Argo Sun-Crichton that it could be verified that Sebacean women do not experience the same phenomenon.
An analogous real-life example would be the relationship of the Neanderthal subspecies (Homo sapiens neanderthalensis) to the Anatomical Modern Human (AMH) subspecies (Homo sapiens sapiens) of the Human (Homo sapiens) line.
Humans being the ancestral line of Sebaceans and Interions, it is likely that these other species (if they can be considered species rather than subspecies) are also descended from the human stock used by the Eidelons to breed the Peacekeepers.
It is also possible (and probable) that Sebaceans and related life forms display phenotypical variation like eye, hair and skin color that differs from the variation present in humans on Earth. This may mean that the various "Sebaceanoid" species encountered are genetically Sebacean but for some reason underrepresented in Peacekeeper Service, possibly due to racial purity regulations. Several Peacekeepers including Commandant Grayza and Nurse Froy wore exxagerated makeup but were nonetheless incorporated into Peacekeeper service.