As of Solaris 9 logging on UFS filesystems is on by default, you don't need to specify it in vfstab, and to turn it off (in vfstab) you would specify no_logging.
Looking at our systems, I think logging is on by default for all ufs filesystems starting with Solaris 10. At Solaris 9, logging is on by default only for terrabyte filesystems. I guess you have all huge drives. "man mount_ufs" gives the rules for each os.
No, it's default in solaris 9 on UFS filesystems, though maybe not in the early releases. That was one of the contributing factory to the veritas on encapsulated root disk cpu panic/cyclic reboot problem and why the temporary workaround patch explicitly put no_logging in the options for the root filesystem.
I probably wouldn't even have noticed but I had over 200 of them do this to me after a power and ups failure about 12 months ago. When logging was manually removed from vfstab and it was still ocasionally happening I went looking and found that logging was on by default.
[EDIT] Logging by default on UFS was introduced in patch 113073-09 on solaris 9.
The option to turn it off is nologging, not no_logging as I previously posted.