I'm certainly not the best to talk about this, but I'd say it's not going to work well with Mach3. Mach 3 only supports one spindle, so without some form of logic external to mach, be that a more mechanical/electronic or processor form, along with various macros to control things, it won't work.
I'm sure Mach 4 could manage it, although probably not the Hobby version, however it would be best to post over on the Mach Yahoo Group, as Brian is more likely to respond over there than on here.
Regardless, I'd say you're going to have to do a reasonably amount of custom configuration/programming to implement all the typical dual spindle functions.