The titan 12T motor is only rated up to 8.4V so youd be pushing that motor beyond what its rated for and that particular motor isnt known for lasting that long in the first place. Can you do it? Sure. Will it burn the motor up? Eventually it probably would. Whether thats 3 months later or 3 minutes later I can't say but it will take a toll on it.
Another thing to consider is the Dewalt batteries are lithium ion batteries as opposed to lithium polymer. Li-ion has a much lower power density than LiPo so you might end up damaging the battery as well as the motor. I can't say whether or not a Li-Ion has enough power density to power a 12T brushed motor in a rig but my guess would be it might but youd be pushing the battery pretty hard as well.