Since everybody seems okay with the idea, I'll list all the tags that I think we should use and everybody is more than welcome to add any they think would also be appropriate, so for every faction:
Heroes:
[Faction] Hero
[Faction] Summonable Hero
Units:
[Faction] Unit
[Faction] Summonable Unit
[Faction] [Unit Type] (Swordsmen, Pikemen, Cavalry, Archers, ect...]
[Faction] [Unit Level] (Heroic, Elite)
Finally, I'd like to mention that summonable unit/heroes should still inherit from regular unit and hero categories. The summonable categories do not replace the regular categories, it merely adds on.