A Univibe was originally an attempt to imitate a Leslie rotating speaker, yes. While it didn't do a terrific job at that, it became an important effect in its own right, courtesy of Jimi Hendrix, Robin Trower, and others. Trower's "Day of the Eagle" and "Bridge of Sighs" feature a Univibe. Basically it's a combination chorus/vibrato pedal. If you go to Digitech's flash demo for the EX-7 you can get a taste for how that pedal imitates the Univibe anyway.