The gnugk ebuild does not install the addpasswd utility. It is needed to add passwords to gnugk ini's (e.g. addpasswd gnugk.ini foouser barpass). Adding the addpasswd target to make does the trick. Diff follows.
Created attachment 29754 [details, diff] diff from gnugk-2.0.6.ebuild --> gnugk-2.0.7.ebuild with addpasswd
fixed in 2.2.1 and 2.2.2