There is no udevcontrol man page in gentoo udev ebuild. udevcontrol is described in udevd.8 man page, and udev's make install contains this code: ln -f -s udevd.8 $(DESTDIR)$(mandir)/man8/udevcontrol.8 But since gentoo ebuild does not use udev's make install but rather has its own stuff, you need to do the same (i.e. create a udevcontrol.8* -> udevd.8* symlink).
The bug is valid for both udev-087-r1 (current stable) and udev-098 (latest unstable).
Created attachment 96200 [details, diff] udev-098.ebuild.patch
fixed in 099 release.