Yes, you should be able to install "vanilla" Duplicity via apt-get install duplicity and not have it interfere with TKLBAM's Duplicity. At least, that's the way it's supposed to work. If anything breaks it's a bug.
TKLBAM uses a patched version of Duplicity, packaged into tklbam-duplicity, which is a dependency of the tklbam package:
Duplicity and tklbam-duplicity can happily co-exists
TKLBAM uses a patched version of Duplicity, packaged into tklbam-duplicity, which is a dependency of the tklbam package:
The best way to find where a package's files live: