The AIX version should be there as “mk_db2.aix” it is the older one i think 
One of my customers is using the DB2 plugin on AIX but i cannot say anything about the setup and versions as I’m not know anything about the AIX systems.
@jstallsmith in your case it looks like it find only the instance and version. I would do a test with the next steps the script is doing in a manual way. Like
db2 list database directory on $HOMEDIR
The homedir can be used explicitly or you try the mechanic from the script.