it looks the official page for the Buffalo Heart Award is their
facebook page.
the two relevant comment there about the award's criteria are:
- It has been presented each year since to the Buff who demonstrates grit, determination and toughness.
- To this point in the award's history, it has always gone to a senior who has just played his final home game.
It mentions the award is granted each year, but doesn't limit the criteria of consideration to this year's performance. Assuming the full CU playing career is accounted by the voters, I don't think there's a strong case for anyone besides Landman. This position is supported by a scan of the official CU press releases for the last three winners -- they all speak to the player's full career, not just the season in which the player won the award.
Broussard would apparently qualify, as the second point above speaks to conventionally what has happened and not as a requirement. that being said, it would seem he's a long shot.