According to ESPN the TIE-Breakers are determined by the following:
Two Clubs
1. Head-to-head, if applicable.
2. Best won-lost-tied percentage in games played within the conference.
3. Best won-lost-tied percentage in common games, minimum of four.
4. Strength of victory.
5. Strength of schedule.
6. Best combined ranking among conference teams in points scored and points allowed.
7. Best combined ranking among all teams in points scored and points allowed.
8. Best net points in conference games.
9. Best net points in all games.
10. Best net touchdowns in all games.
11. Coin toss.
Based upon the my quick analysis, The cowboys and Seahawks do not have 4 common opponents in order to determine the tie-breaker, therefore it would revert to the Strength of Schedule, upon which Dallas has the edge. Bottom Line, if Dallas wins out they should capture the #2 seed.