So you use something like custom events (callback object) and which functions are registered to certain event is based on player location? It sounds interesting.
I have tested which events occurs when you enter/leave campaign and it seems that mentioned "EVENT_PLAYER_ACTIVATED" is the best choice. There is no campaign event that you can use and "EVENT_ZONE_CHANGED" is triggered way too often (for every point of interest on the map).
To find out if you are in campaign I'd probably use:
Lua Code:
if GetCurrentCampaignId() ~= 0 then
d("You are in Cyrodiil.")
end