On the other hand, ssh is a very robust protocol and somehow ssh sessions seem to readily survive disconnect/reconnect cycles. Making use of this, it is possible to get a workable, if slow, connection to a passworded-and-sleeping Mac.  On one connection to the firewall machine, run a loop of the wake-on-LAN command so that the magic packets that make the Mac wake are being sent every second or so.  Use another connection to ssh into the Mac and do whatever you need to do.  It helps to plan out what you need to do so that you can get the commands in fast, but even during the cycle where the Mac goes back to sleep and gets reawakened by the wake-on-LAN loop, you can type commands; they just won’t appear (not even echoed) until ssh recovers the connection.

While this is an annoying way to use a machine and it’s probably not good for the hardware to cycle in and out of sleep repeatedly in such a short time span, it does give a way to get at a passworded and sleeping Mac remotely.