What if I want to use a different MPEG 2 encoder instead of the Main Concept encoder inside of Premiere Pro. Can I just output a Cineform AVI and then load that into a program like CinemaCraft or Procoder?

Generally yes, CineForm AVI files can be loaded into any Windows tool for encoding into MPEG2 or any other export format.

What if I want to use a different MPEG 2 encoder instead of the Main Concept encoder inside of Premiere Pro. Can I just output a Cineform AVI and then load that into a program like CinemaCraft or Procoder?
If you have Procoder 2 it plugs into PPro and works fine with CFHD. Be sure that upper fields is selected and 16:9 with a pixel aspect of 4:3 is used and it makes great mpegs. If you have Procoder express then you will have to run it standalone and use a single file. The main Concept encoder is very limited compared to procoder.