Does the artist retain copyright on images submitted to the print
program?
Is the print program non-exlusive, i.e. can I still sell prints
using other outlets?

The artist is not transferring any copyright only permission to
reproduce prints - from the terms:

5) The Artist grants permission to The Artists Web and Easyart to
reproduce prints of The Images submitted for sale as outlined in
this agreement and in addition The Artist grants permission for
The Images to be displayed on their respective websites.

In addition the print program is non-exclusive so you can sell
prints from other oulets at the same time.