OK, but what version of OS X? 9.2.2 will easily connect with everything up to Leopard. Snow Leopard breaks it.
ALSO: Porter, I don't know that much about Basilisk II, it may well bypass the host OS. I have been trying to get Paul Pratt to do something like that on Mini vMac so that it would grab the serial port and actually push AppleTalk over a USB/Serial adapter just like a real 68K Mac. Of course if that were possible then one could also grab the Ethernet port. However, Paul seemed to think that was not very likely while OS X was actively accessing the hardware, which would require more complicated implementation, if it is even possible. However, I am pretty sure SheepShaver won't access the Ethernet framework, if only because I have not been able to do it. Perhaps with the correct low-level UNIX commands it might be possible.