You're jumping the gun a bit... the main problem is that they can't secure their main computer, since they require dictation to work in order to enter passwords. For the main login screen, the dictation software isn't loaded yet.
If they can password-less auto-login to the main computer, then use their dictation software to load up a VM, that VM could be considered secure.
As a side note, can't you also run Mac OS X as a VM guest from a Mac OS X host? I thought that Apple made that license change a while back. If that's the case, they could keep it all Mac, if they'd like.
He can type things using dictation and that would presumably let him log into the VM, his problem is that the dictation won't work for the OSX lock screen.
The idea probably has some other practical problems though.
I don't see how that would make it harder. Audio surfing is easier than should surfing. Wonder if he could somehow get his one-button clicker to translate morse code into ascii. Then he really could log in in a fairly secure way.
Audio eavesdropping could be pretty easily defeated with a challenge/response system. And if the speech recognition system is powerful enough, the response to the challenge could simply be to repeat the challenge in your own voice - which would be really user friendly.
I don't think he's trying to make it more secure, just trying to get a minimum level of security where he can open the laptop and input a password. Right now, the OP is unable to do that due to OSX not allowing any applications to run at the login screen.
If they can password-less auto-login to the main computer, then use their dictation software to load up a VM, that VM could be considered secure.
As a side note, can't you also run Mac OS X as a VM guest from a Mac OS X host? I thought that Apple made that license change a while back. If that's the case, they could keep it all Mac, if they'd like.