The counterparter LUKS="yes" to parameter --luks is not mentioned in /etc/genkernel.conf. Please add it.
Commit in Git, needs mergin to master. http://git.overlays.gentoo.org/gitweb/?p=proj/genkernel.git;a=commitdiff;h=d592f0602ab9b3e04537bb32565019570d4a2733
Merged to master.
Included in 3.4.10.908, closing.