I'm trying to control an fx plug-in using a midi controller and record/automate the midi.  Should I use the 'Configure as Synth' feature?  If so, I'm not sure how this works, how it affects the plug-in within the project, or how to set it up.  Any info would be appreciated.

It may be helpful to know which plug-in(s) this is about.
 
Starting with X3 it is no longer necessary to configure FX plug-ins as synths. FX plug-ins that accept MIDI data have the "Enable MIDI Input" option available on the VST2/3 menu in the standard header.

 
Once enabled, the plug-in will appear in MIDI track output drop downs.

Thanks for the response.  I'm using the NI Rig Kontrol pedal with Amplitube 4.  I also tried Arturia Wurli V just as a test.  I tried midi input via usb and the midi out on the pedal, but midi learn is unresponsive.  The midi icon is still lighting and also the midi led on the pedal.  Looks like midi is being sent and received.

The basic setup for a MIDI controller to communicate with a plug-in using MIDI learn is as follows
 
The controller (the NI Rig Kontrol in this case) is setup as a MIDI input device in preferences
An audio track has a plug-in (Amplitube 4) in the FX Rack with "Enable MIDI Input" checked in the VST menu.
A MIDI track has the input set to the controller, output set to plug-in and input echo is enabled.
 
Enable MIDI learn on the plug-in control and send a signal from the MIDI controller to train the plug-in control.
 

Looks like I needed the input echo enabled on the midi track.  Thank you very much, I've been fighting this for a while.