Seahawks will be able to run the ball against the Rams. The 49ers couldn't last week because of the scheme they run on running plays, which is generally shut down by stacking the box and filling gaps. Seattle does a lot more zone runs and Lynch is often his own lead blocker, and coming out of spread formations they will definitely have room in the middle.
If Bevell doesn't stick with the run I wouldn't blame him given what Kap did to them last week in the air, but that was down the field stuff and Seattle doesn't do that all that much. If I were him, I'd use 3WR sets or 2 TE sets to spread their front horizontally, and then run the ball in between the tackles with Lynch over and over again.
Bottom line is I'd let the defense win the game for me. No point in taking risks on offense when you have such a good defense. The Rams are not the Cowboys offensively.