I am doing a similar setup with luks and unionfs.
adding nofail to the options of unionfs either in gui or fstab does allow the system to boot instead of crashing to emergency state.
However after unlocking the luks encrypted drives the shared folder will not mount with nofail in the options of unionfs. I have to remove it and do a mount -a for shared folders to work gain.
Any ideas on how to fix this? or a workaround?
I really wanted to commit to encryption and get myself used to it.