Nmap lacks zenmap, which is a major new feature: http://nmap.org/book/zenmap-topology.html
It would be cool to have an UES-flag to enable it!
Are you sure that it lacks zenmap. It installed zenmap on my ~x86 system.
You need USE=gtk to get zenmap. With USE=-gtk, you only get the CLI tools.
Strange, was the ebuild changed silently without bumping? Now it's there.
FYI, I compiled with USE=gtk, it's even in my bash history!