I am setting up a case in Gambit and I am trying to define the zones where the remeshing is occuring. Are these defined as interfaces? Should each zone have separate vertexes and lines? This is a 2D case.

You just define them as different 'continum type' by selecting the moving zone and then rest of the domain.

Note that (In Fluent) if you are defining it through a profile, then you need to select these zones as per the profile you have already read to specify the motion.

Hope that helps.