I just installed app-cdr/gtkcdlabel-1.0_pre7 and it pulls libcdaudio in without any use flags to control this behavior. However the website states that "Features * Doesn't require libcdaudio to access the CD drive or access freedb.freedb.org" and says "If you want to run versions prior to 0.7.0 then you'll also need libcdaudio". Could it be that this is an old dependency in the ebuild from pre .7 days? Apparently libcdaudio should not be mandatory for this ebuild. Thanks for examining.
Thanks for the information. The ebuild is now updated.