"Wrong ufstype may corrupt your filesystem" - Should I be worried?

This message could be generated when the user or a script runs the update-grub script, which would explain why you get it after kernel update. From what i understood, update-grub tries to dynamically find all the possible partitions and operating systems in them for generating the most complete grub.conf file. one of the options(one of the last ones actually) that update-grub tries for mounting an unknown partition, is ufs. This is a bug however as it could be misleading and confuse the user.

More info: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1374759