I've been working on this for a little while, today, and have decided to wipe and go back to JF's 1.42 build as I had before the cupcake upgrade. I'm going to try this all again from the beginning and make sure root works in 1.42 (and Debian installs), then wipe and go to 1.5 and try the install again.
It seems that the newer SU whitelist occasionally breaks root, so I've read. It seems that it wasn't only Debian that was failing for me. Other root commands were denied permissions as well. I'll post back with any news or progress.
UPDATE: No joy!

I was able to install Debian under JF 1.42 (US), but after wiping and flashing to JF 1.5 (US or ADP1) there seems to be something that breaks in the new SU Whitelist app (in either version, with or w/o formatting). chmod attempts result in either Operation not permitted or Permission denied.
New question... Would it most likely be a problem with root, the SU app, or busybox? I am torn now, between my love for Cupcake (the ADP1 version was marginally faster and better on battery consumption) and my desire to run Debian.

I would love to get this fixed if there is anyone willing to help.