How are you actually seeing them? Dies Diei? Should never be visible to anyone other than the Sidar player... The no experience is because they're not a combat unit, nor are they supposed to ever be involved in combat.
Yes, Vehem, I do have Dies Dei. However, I am definitely able to see the Souls in Sidar territory as well as mine. The Sidar are up against my eastern border and sending these things (and Ghosts, of course) allover the place.
It is interesting that that they are not a combat unit, yet listed as having 10% strength. Also, they seem to be able to defend cities, but I'm not sure about that. They can be 'killed' - I've killed dozens of them.