gproftpd does not use the openssl library nor does it have the configure flags --with-modules as used in the ebuild.
gproftpd uses openssl as a binary (it runs the openssl command) when generating certificates, but it can compile without it and also run without it. If user wants to generate certificates, he should also be able to use them - that means that net-ftp/proftpd has to be compiled with openssl support, and in that case the openssl binary is also installed.
Patch for tested ebuild in attachment.
Created attachment 416616 [details, diff]