I could be mistaken but it seems many other themes aside from gnome-icon-theme properly support all icons demanded by remmina. perhaps virtual/freedesktop-icon-theme is a better dependency here. Reproducible: Always
Created attachment 386806 [details, diff] ebuild patch for remmina-1.1.1.ebuild
https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=38be4f0caa42aa9472632bf90fc6c8a2555bb5c9