I'm not quite sure what you're asking. Ssh is just a program you can use to connect to remote machines. You wouldn't replace one of your virtual terminals with it. Why can't you just login to the virtual terminal and run ssh? Or use the terminal emulator in your desktop environment? To actually change what would run on the virtual terminals you would probably have to modify the getty source code -- I don't know how well a normal program would take to just being set to listen on a virtual terminal -- an interesting thought though!
Maybe if you try to tell us why you're trying to accomplish this it would help a little more. It is an interesting question though (assuming I understand what you're trying to do right).