As of EAPI=4 , the perl-module eclass will automatically *DEPEND on perl, unless GENTOO_DEPEND_ON_PERL=no is set prior to the inherit line. As such, the optional dependency via perl? use flag doesn't actually work. Also, an emerge of this ebuild should be tested on a system with no perl installed as I *think* that all the perl-module functions should only be called when USE="perl" is set...
Fixed, thanks!