If a moving gate (from the Lurker at the Threshold expansion) would move into a vortex in Dunwich, what happens? My best guess is that, since the rules say it moves as a normal monster, it moves into the vortex, and, like a monster, adds a horror token to the track.
Moving gates cannot move onto Vortexes.
From a post on Fantasy Flight's forum:
Gates can't enter Vortexes. In this situation, the vortex is treated like an open gate, and gates can't move onto gates.
If a gate has to move into a vortex, it just stays in place instead.
I do not believe that the answerer, Tibs, is an official representative of Fantasy Flight. However, he has nearly 4000 posts in their Arkham Horror forums and seems to have a very good grasp upon the rules.