[Abagail]

If you don't need to use teams elsewhere, you can have everyone on the same team always. This prevents most player-to-player damage and iirc OnPlayerTakeDamage is still called. You'd have to set health/armor on your own though using (SetPlayerHealth/Armour) when taking damage.

FLOAT_INFINITY also could work as mentioned, is essentially unlimited health, although this means you can't use GetPlayerHealth on wounded players.