I wouldn't worry about it from a loot perspective. I never worried about having rogues in the party in either Origins or Awakening and I never felt like I was missing out on any worthwhile equipment. You can always get the same caliber of stuff from shops or looting corpses.
Besides, you can do the main quests in any order, so if you like you could pick up Sigrun right near the beginning.
That said, Nathaniel Howe is an awesome character and you should give him a chance.

I really felt that the characters were a lot deeper and more interesting in Awakening despite the shorter running time, and he is a prime example.