Artifact/Nexus guards can give RP I just do not know how to make them do it.
The first one to aggro them gets RP (afaik). Similar to Warden and Ranger.
I'd say Shirley/Hera shouldn't drop anything. There isn't even a quest to destroy it. Guess why? It's a map for new players. They are introduced to escorting there. Having geared players destroy it (remember, it only has 70k HP) would ruin that.
In Viledon, they're introduced to PvP fights around escorts and destroying the other escort. Having them drop stuff would make more sense. Obviously way worse than in Nemesis (1G, no or very few pet drinks, etc).
I don't agree with all alert suggestions. Noticing that your stuff is under attack (and alarming others if needed) should be done by players themselves.
However, it would be okay for events that everyone can see already anyway, like nexus destruction (you can see it on the map) or destruction of escorts (quest will fail).