As an owner of multiple MacBook Pro machines, Hackintosh user, and general lover of complex solutions, I have tiptoed down the path that you're planning to explore.
I have run Win7x64 as a guest OS under Mac OSX (both Snow Leopard and Mountain Lion) using VMware, and I've run Snow Leopard as a guest OS under Win7x64 using VirtualBox. In both configurations I succumbed to the temptation to invoke a DAW within the guest virtual machine while running another DAW in the host/native environment.
The upshot of my experience is that this isn't a useful or stable way to do audio. The central issues seem to be related to the timing/latency problems of a virtualized physical port. There's no equivalent of 'bridging' that hypervisors can use for network interfaces to handle the tight bond that drivers would need to handle firewire and USB ports. Therefore, audio streams (and MIDI streams to a lesser extent) coming in via USB have a particularly ugly data path because the half-duplex USB hardware gets managed by an asynchronously dispatched virtual machine.
I don't want to be Debbie Downer for you (my friends think I'm a painfully optimistic person in general) but the close marriage of the DAW with the audio/MIDI I/O, along with the close timings needed for reliable read/write to the disk/SSD argue for using conventional methods of running parallel DAWs.
One thing I didn't try is the use of an Ethernet-based 'sound card' feeding the guest OS, while a conventional firewire/USB 'sound card' feeds the host/native DAW. In that way, you might circumvent the typical problems that the hypervisor throws in your way, while linking the two DAWs externally via the 'sound card' hardware. That, along with a regular MIDI splitter feeding the disparate inputs may be a way forward.
Grr…you've got me thinking about this again…!
Happy Trails.