Heads, yes, but you may need to drill some holes a little deeper as the double ended neckball of the HACKs figures tend to make the MTF heads sit a little too high, but for the most part they are compatible.
Legs, yes. You have to heat up the HACKS thighs to pop out the innner thigh but the hip balls are pretty much the same fit wise. MTF hips should just pop off but you can warm them up real quick to swap out.
Torsos, not so much. MTF have solid torsos that connect to a ball peg in the waist. Meanwhile HACKS have a much more complicated system that works great with other HACKS parts but won't translate to other figures without some modifications.
You can kind of get a better idea about the construction differences here, but that MTF exploded view doesn't accurately reflect that the torso and waist are each solid pieces and not easy to crack/cut open.
http://wiki.joecustoms.com/wiki/Figure_Construction