I play multiplayer and Co-op with my boyfriend on the same Xbox console. I was thinking of getting the season pass for the DLC but would I need to buy two, one pass for each of us? Are they just registered to your accounts or will the DLC be available on the console for us to both use?
If you are both always playing on the same console, then I don't think it is necessary to build two season passes.
All DLC and XBLA games have the following licensing restrictions:
So as long as all the Gears 3 uses the standard Xbox LIVE licensing (I don't see why it wouldn't), then you should both be able to use all of the Gears 3 DLC assuming you are both always on the same console.
As an aside, at least for the Versus maps (not sure about Horde mode), but as long as the host has the DLC then everyone can play on the new maps (even if they don't have the DLC).