I just finished upgrading from FC9 to all the latest and greatest rawhide packages and got a similar problem. When booting it kept cratering when the volume manager tried to mount a logical volume located on a software raid 5 device. After I removed the partition from my fstab and rebooted I was able to determine that my raid 5 device was being created a /dev/md127 rather than /dev/md0. After stopping md127 and manually recreating it as md0 I could then mount my logical partition.
Doing some searching it seems that the initrd may be at fault. One post I read indicated that if your / partition can't be read for some reason then md will not be able to see /etc/mdadm.conf and read the proper device id out of it. That doesn't seem likely in my case as I can boot off of /.
I have also read some other stuff indication that your mdadm.conf should be in your initrd. Mine most certainly is not. You can check yours
zcat /boot/initrd-<version>.img | cpio -i *
Then also check
And see if there are any references to your raid device in there. Again I don't have any. I tried doing a mkinitrd on my working system to see if that would help and it didn't. So there could be an issue with mkinitrd. It looks like the people using dmraid are having issues with mkinitrd. You can look at
for more info on that. It may also give you some clues of where to look for clues.
I am sorry I don't have a better answer for you.