I've gotten in the habit of using a voodoo kernel after I flash a rom and then flashing setiron over it. When done this way /system gets converted and stays that way even when you start using ULF.
you can check by typing
Mount | grep ext4
It will list all partitions that are ext4
Just wondering if ULF will also convert /system.
In general usage, /system is in read-only state,
so I think it is nothing helpfull to convert it to ext4.