In my testing, I have found a way to enable SSH in Single-user mode (SUM).  So far, I have only been able to make outbound connections.  Even though the SSH service is on and the ports show as LISTENING , I still am not able to remote in from another machine.  But I can use the machine booted to SUM to SSH into another remote device.

Below is the script I save as /var/root/.profile , which loads everything automatically.  These commands could easily be entered manually as well.  This script is based off my Single-user Mode Intrusion Detection script.