Hey ajcgi,
Thanks for spotting that, one of the reasons for putting the script out there was that others users would try things I wouldn't necessarily think of testing - like rendering planets!
I've attached an update to the script, try it out and see how you get on. Also included some scene files used to test it out.
Couple of notes about the script:
The script was written so that everything should work with the default setup in Terragen, so you don't have to adjust anything to get the pipeline working (well, not now hopefully).
For instance, a default Terragen camera uses "Use horizontal fov" as its Perspective setting, you don't need to change this, just adjust the Focal length for your shot. (although when writing out a .chan file, Terragen converts the fov to vertical before exporting).
When you import a .chan file into Terragen it changes to "Use vertical fov". Leave the "Source rotation order" to "ZXY (Nuke Default)".
When you import a .chan file into a Terraman Basic Camera in Maya, the rotation values might look different, as the script converts rotation order on import.
I changed one of the rotation orders in the import camera in the script and it works with your scene now, though on your original camera it's a bit off. I think that may be a precision error since the camera is so far away from the origin.
There's a good page on it in the Terragen Wiki.
They suggest making sure the North Pole of the planet is centred on the World origin to minimise any problems with coordinate accuracy, so I tried it in a new scene with the recommended position and it lines up well between Maya and Terragen. (MarsNew_v01.tgd).
I'd also try on of the smaller scales when importing the planet - like 1:1000 or even 1:10000, you can always export the Maya camera manually and scale it up for the 1:10 scenes.
Have a go with it (try with a new Y position of the planet), please let me know if it works.
Get the test files from:
https://dl.dropboxusercontent.com/u/81475291/mars_scene_files.rarDG