As far as I'm aware crawler motors are designed for torque density, efficiency, and smoothness as opposed to a more normal 540 motor which will be engineered more for higher RPMs. I'm not sure if these are the only differences but thats some of them. Basically theyre just engineered with...
If you're going to use it with a brushed motor then yeah, should be fine. Just make sure it has an LVC if you're going to use it with a LiPo. Or at least get a low voltage alarm if it doesn't have an LVC
It will fit. How much of a tight squeeze it is and how you have to run the motor wires may depend on the motor. Wicked did make his Castle brushless motor fit and Big Squid made one fit so it is doable.