No, a man cannon is an immovable object. Even if you somehow magically managed to get the man cannon spinning through some incredibly complex maze of gravity lifts and man cannons as soon as you saved your map it would stop in place. If you are trying to figure out a way to have the same effect then PM me the details and i will see if I can help. ~ForgeGod117~
Yes, you can do this with grav lifts but not mancannons. A fine example can be found in Cosmic Rick's map Electric Slide. Behind the constantly-moving dumpster is a rotating grav lift.
Yea, Swordscar discovered it more than 6 months ago, I don't remember if he posted it on FH or not, it is on H3A though