/usr/share/doc/udev-135-r3/html/writing_udev_rules.html from sys-fs/udev-135-r3 mentions a binary called udevinfo. According to bug 236551 comment 7 that binary has been deprecated, removed, and "udevadm info" should be used instead. Upstream git seems to refer to this outdated command as well, and I'll try to write to the upstream mailing list about this. Still, a simple sed in the ebuild should fix this, so it might make sense for gentoo to address this on the distro level.
that's probably better to address this upstream first indeed
Upstream thread: http://thread.gmane.org/gmane.linux.hotplug.devel/13635
Patch applied upstream. Either apply http://git.kernel.org/?p=linux/hotplug/udev.git;a=commitdiff_plain;h=04f2a4fb6eded359cc8be1ba4ce33d7f7db6919f in the ebuild, or mark this WONTFIX, UPSTREAM or similar, and wait for the next release from upstream.
Added this patch to udev-135-r4.