The code that recognises tamed versions of hostile mobs, that are owned by players, that is applied to player owned npc's so that they do not attack them, should also be applied to friendly Tribal or Nation npc's to stop them targeting the same tamed player mounts.

To stop situations where a player arrives at a friendly Nogg or Guardian town for example:

"Hello, ive come to trade!"
"Thats great, and welcome, but just wait there while we slaughter that Hippogryph or dragon you rode in on............."

: )