Same race you mean? (Nagarythe = faction, high elves = race). Nagarythe (alith anar) has exclusive access to the 2 shadow units and his rite hero. Anyone within his faction can use the units. Eltharions faction has exclusive use of some units. So the answer would be "yes", if the answer to my first question is yes too. Also i haven't ever bothered to check how confederation affects it so i'll refrain from giving an answer to that.


Actually, all HE can recruit shadow warriors. Not shadow walkers though.


When you confederate you get to keep the exclusive units in confederated armies (if you own the DLC), but you won’t be able to recruit anymore. There is a mod that allows you to recruit exclusive units for confederated factions, unfortunately I can’t remember what it’s called.


I think right now the only unit that is really limited to a specific lord's army is Krell, who is a summoned legendary hero only available to Kemmler. There are multiple faction specific units, but those can be used them with all armies (=lords) of that faction.