Munkiimport is run interactively by default, but there's also a --nointeractive option.
I am a total novice at Make, but you could define new target like 'munkiimport' with a requirement of 'dmg'. The 'dmg' target is defined in The Luggage's luggage.make and outputs to ${DMG_NAME}. So we can just pass this to a the new target that invokes the munkiimport command.
Then we can just say "make munkiimport". For example, for a Makefile that would normally just package up a postflight script in a bundle package:
include /usr/local/share/luggage/luggage.make
TITLE=My_Package
PACKAGE_VERSION=2014.10.16
PAYLOAD=pack-script-postflight
munkiimport: dmg
munkiimport \
--nointeractive \
--subdirectory apps/My_Package \
--displayname "This is my package's fancy displayname" \
--description "This was imported via The Luggage" \
"${DMG_NAME}"
Tim