Does the Digitech unit provide added sustain?(like those Gary Moore infinite fedbacks/sustains)
Yes and no. It doesn't drive the string like an E-Bow or the Fernandes Sustainer do.
It analyzes the vibration of the string and generates a very natural sounding feedback which lasts as long as the string is still vibrating. You can get a very long sustain/feedback when you keep the string vibrating using finger vibrato etc.
As soon as you mute the string the feedback stops.