They dress like nurses. They often joke about asking for payment.
Altruist elves are likely the most "good" of all elves (assuming Erfworld has some concept of alignment, and good/evil troop types). They either possess a regular troop type with healing ability (seemingly rare) or a high number of Healomancy casters. This likely comes at the cost of any sort of combat ability. Indeed, their healer types may be incapable of dealing combat damage. They likely pop no warlords at all, leadership being handled solely by casters (and thus offering no combat bonuses). Altruist elves may also shun tribute/pay/spoils when accepting an alliance, preferring to support themselves - though it is unclear how they would do this, as they need money to pop new units, and so must have some source of income. Perhaps they are unique among non-capital sides and have a small permanent income, or perhaps they exist upon charitable donations, or some sort of nominal tax on all sides.