It took me a while to figure out that the initrd doscsi option was necessary when SCSI support in kernel is built as modules. I'm attaching a quick patch to add this option to the genkernel man-page.
Created attachment 123199 [details, diff] Adds info about option doscsi to genkernel man-page
OK. I've added this to SVN and it'll show up in the next genkernel release.
Please test genkernel 3.4.9_prer1 or better. This should be fixed now.