Never underestimate the draw of Fantasy Football, or just a football game in general. It might be the only professional sport in the states that draws conistent viewers regardless of the teams.
Look at the Thanksgiving games. The Lions play on that Thursday every year, and they are terrible, yet they still get great ratings year in and year out.
You might be okay getting there as the hockey game starts, but I think it would be a safer bet to get there before the football game starts. Chances are, they will have the football game on the big screens and half of the small screens. To watch the hockey game, I'd suggest sitting at the bar or at a table where there are two TVs right next to one another, that way, you're less likely to get anyone caring about what is being shown on the TV you're watching.
And, yes, let them know that you want to watch the hockey game when they seat you, if you opt to go into the restaurant side of the joint. If they have that game on somewhere already, they'll put you in a section near that TV or change the channel on a TV to accommodate you.