Mercenaries maps can be played on following modes:
Mercenaries
Survivors
Onslaught
Predaotor
Siege

DLC list:
Survivors Mode
Onslaught Mode
Predator Mode
Siege Mode
Ada's Campaign with Coop
No Hope (Hardest Difficulty)
Stage Map Pack A
Stage Map Pack B
All Stage Maps Bundle
All Modes Bundle
(every single mercs map is listed individually, including ones which are already in a game, that's probably lines they forgot to remove)