Most of the unit traits are pretty much the same for all factions. Charge is available to all units, mounted.. foot, whatever. Obviously it's more useful on mounted though.
Some are restricted by race, for example "Zealot" is for Wraiths only. I don't think it's documented anywhere though. If you really wanted to investigate open up the file "CoreAbilities.xml" and search for them all in there. You'll find a "PreReq" tag on some of them.
If you happen to be playing a mod like Stormworld, that has a handful of race specific unit traits.