User blog comment:ShawnCognitionCP/The Empire vs Stormcloaks, the most likely answer/@comment-3407280-20140612232511/@comment-24728100-20140613031807

The Dossiers meaning is pretty clear, they would try to aid either side if one got an advantage over the other, otherwise their policy as they say is hands off.

Most people skip right to the part where it talks about Ulfric being assigned as an asset, they don't look at the fact that this dossier labels him both dormant and uncooperative in this asspect

NOTE: the Dossier mentions something many to this very day have missed:

The so-called Markarth Incident was particularly valuable from the point of view of our strategic goals in Skyrim.

''The *_Markarth Incident_*, many don't know that this was when the empire betrayed Ulfric and his supporters and created the first reason to Rebel... this was an imperial action, one the thalmor call *_particularly valuable_*''