I had the same problem with the Xbox 360 version of Skyrim with the enemies not showing up at Fort Dunstad. I could not reload a save before the quest was given so I thought that I couldn't complete the quest. However, I did not finish the main quest before this. Upon completing the main quest line, the quest titled "Battle for Fort Dunstad" showed as completed in my quest log as well as in the completion of regaining the Pale in "Reunification of Skyrim". No quest markers were available at this point, but after talking with General Tullius back in Solitude, I was finally able to continue on the quest for the Imperial Legion. I hope this is helpful! 50.133.149.222 05:21, July 15, 2014 (UTC)