I ran the command adinfo -A -u [username] with my domain credentials, and it DID prompt for a password and said the password is correct. So that works great.
The su is where we broke here. I tried the command "su - [username]" with a domain user, and got the following errors:
su: warning: cannot change directory to /export/homes/[username]: Permission denied su: /bin/bash: Permission denied
This is basically what we've been seeing across the board since getting this far and where we've been stuck.
We'll continue digging, I think you gave us a lot to read and a lot to work on. I appreciate the support and would, of course, love to hear your feedback when you have time.
Will post updates as we make progress.