Though there is much effort to classify the sentient races which have begun to explore the Aetheria there is in truth as many races of sentient life as there are realms. The division into categories or species is mostly for the ease of communication. However it is also true that most sentients like being able to sort those they meet into neat little boxes in their minds.
The species classifications are sorted such that creatures with similar physiologies are put together, though ideologies might be vastly different. In fact within some species there are races which often appear within predator-prey arrangements within the realms. The issue with these differences is that they are formed into diplomatic unions in Corazons, therefore similar looking races with radically different ideologies must somehow work together to negotiate for the betterment of all their races.
Within realms breeding between the little sub-categories or breeds is mostly infertile and between categories is always infertile. This is often argued as the basis of the categories, but has little effect out in the raw aether.
Within most realms cross-breeding between the species is rarely an issue as there is generally only one species native to the realm. In fact in some realms only one breed is present. Therefore most sentient races are not aware of the consequences of such cross-breeding.
Within Aetheria there are no restrictions, the extreme aether saturation leads to extreme fertility in both females and males of all species. Sentients will find themselves easily able to reproduce with those of their species, when before it would have been harder or impossible. They may even find themselves able to breed across the species with fertile results. Physical limitations will often apply such as size differences or fertilisation and gestation methods, but love can and will find a way.
However cross-breed children are viewed by most cultures as unnatural, soulless or even inherently evil. As such even in the quite open-minded society of Corazon these children are treated as second or third class citizens by most. Some of these children are so obvious that they cannot avoid such treatment. However they may be be able to pass as one of those of their parents breed. If there have been a few cross-breeds that look similar to each other they may band together and pretend to be a new species to avoid ill treatment, this has mixed results as other sentients have become suspicious of this behaviours.
There is so much variation across the aetherverse that none of this should be important, but to the sentients involved it is very much so.