User blog comment:Draevan13/Ulfric's suspicious Thalmor Dossier/@comment-3492791-20121211085216

Just to play devil's advocate, there is really not any evidence that he worked for the Thalmor. Contact and asset do not mean aid and ally. Establishing contact could mean nothing more than simply being approached by an operative, and being an asset is not always wittingly. He could have been being manipulated by the Thalmor, then after the Markarth Incident he may have become unresponsive to manipulation because his focus became going against the Empire, and was thus not as easily strayed from it.

What really interest me about the Dossier is that they refer to it as the "So-called" Markarth Incident, implying that it may have possibly be orchestrated by the Thalmor. Due to that Markarth is the only city in Skyrim to have not only open Thalmor activity, but an actual base of operations, they may have had an influence over Igmund. Perhaps they were able to influence him into asking specifically for Ulfric's help, as he was already a known entity, and have Igmund make the offer of free Talos worship. Knowing that when Ignmund granted Ulfric his free worship that the Empire would have to step in or be accused of neglecting the treaty. This may have been simply to distract the Empire, or maybe even to go so far as to give the Dominion provocation to start another war, but the Thalmor quite clearly gained something from it.