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.