Is Bass Non-Directional In A Two-Channel Rig?

You can, but the timeing would come into consideration.
Give it a try and if you like it, go with it.

Sub bass should not be directional. You should not hear where it is coming from when set up properly. It may take a while to get it right so be patient.

When I first got my subwoofer I had it sitting directly behind my side of the couch via wireless connection. A friend of mine came over to hear the subwoofer and assumed that he was hearing the "before" since he didn't see the subwoofer. He was, however, wondering why I need a subwoofer based on what he was hearing. It's now next to the right channel speaker because the wireless connection didn't play well with my wireless printer or internet connection.

I believe that they have done studies showing that people can't pinpoint a direction below 80 Hz.

It should be non-directional but the timing issues remain, anyway, especially with wireless connections that introduce 10-20msec or more of delay. This can work but putting the sub up front with a wired connection makes it a lot easier.

Kal