When installed, GNATS creates a new user gnats and sets its home directory to .../gnats-adm/config . The last component ('config') is a file. The proper directory would be probably gnats-adm OTOH, gnats-adm is part of gnats-db package and the separation between gnats and gnats-adm package is completely bogus due to the shortcomings of GNATS design, so the problem above is not a big deal...
Gnats is no longer going to be shipped since it isn't maintained any longer. I thought that it would be a good idea to let you know about this in advance. Tim