EDIT: Missed that. Yeah, Green Bay gets in on head to head.
Thing is, if they both win out and get to 10-6, you could have other tiebreakers (against Dallas and Minnesota), which would mean the GB/Sea head to head game wouldn't come into consideration.
EDIT AGAIN: Minnesota would win a tie-breaker with Green Bay for the division if both finish at 10-6. If Dallas, Green Bay and Seattle are all tied at 10-6, Green Bay would be eliminated, having the worst conference record of the three teams. So, Seattle cannot win a tiebreaker with Green Bay, but they would advance in a three-way tie with Green Bay and Dallas.