I stumbled across this:
http://support.apple.com/kb/TA23436?viewlocale=en_US
Its an apple support page basically saying that you can not trust compressor, final cut pro, or quicktime to validate the dimensions of a mpeg2 because they will scale a 720x480 to 640x480 to comply with 4:3 playback. The file is actually 720x480, but quicktime tells you its 640x480.
The article says you can use DVD Studio Pro to properly validate a mpeg2 files actual dimensions. I unfortunately didn't have any luck in this. Using the above posters trick of changing the dimension setting for compressor via text edit, I sent an mpeg2 (m2v) file with dimensions of 720x512 to DVDSP, but the program rejected it as an invalid format. I then reverted the dimensions back to 720x480, and DVDSP was more than happy to ingest the file. Making it impossible to actually use DVDSP as a verification tool like apple suggests.
So it seems like the text edit trick might actually be working, theres just no way to verify it.