Essentially, you can use any 3D modeling program to model at least the map landscape, but at the end, you must recur to the tools made appositely for MM2 to finish the works. The important, is organize well the objects and the materials, and finally export all in 3DS file format so to be able to import, fix and finish it in ZModeler. At the end, through ZModeler you export a new .3ds file that will have to be adapt to be used with the MM2 City Toolkit program.
I know that the Pro version of Google SketchUp can export in 3DS file format. For the DAE file format, if I'm not wrong, there's a plug-in for Blender which allows to import this file type in there, to be successively exported in 3DS format.
Concerning ZModeler 2, you can use it only for modeling because it doesn't support MM2; once finished the modeling work, it's enough export in the older ZModeler 1 .z3d format to refine the work there and finally export in .3ds for the successive steps in MM2 City Toolkit program. Exists a MM2 PKG filter made appositely for ZModeler 2,
here the topic about it; I haven't tried it, but maybe it's made to export only cars type .pkg files.
