I would give a guarded yes.
In theory, Sun always warns that you should take a server down to single user to run ufsdump on the root file system. In practice, very few sysadmins are able to take their servers down for regular backup.
What version of Solaris are you on? I'm on Solaris 9, and I use fssnap to take a system snapshot before using ufsdump. The snapshot has to be on a different partition. You still want your system to be as quiescent as possible. In principle, you can still have situations where a file is active at the point of the fssnap and is not in a consistent state. In practice, if you are doing this in the middle of the night or when the system is not too active, it seems to be pretty rare that problems occur.
Do a man on fssnap. What you want is something like:
# WHICHSNAP=`/usr/lib/fs/ufs/fssnap -o raw,bs=/usr/local/snapshot,unlink /`
# /usr/lib/fs/ufs/ufsdump 0ufN - /dev/rdsk/c0t0d0s0 ${WHICHSNAP} \
> | (cd ${MOUNTDIR} && /usr/lib/fs/ufs/ufsrestore -rf - )
# /usr/lib/fs/ufs/fssnap -d /
Note the command line continuation on the ufsdump piped to ufsrestore, and you'll have to assign a value or subsitute something for MOUNTDIR.
Of course, you want to read the man pages and fit all of this to your own situation.
I've assumed that c0t0d0s0 is your root partition. It might not be. I've also assumed you have another disk available that has c0t1d0s0 available and in the same size.
The location /usr/local/snapshot is just an arbitrary place where I put the snapshot. It has to be on another partition from / and have adequate space. Adequate space depends on file system activity. It might use very little, or if something large gets changed while you are doing the ufsfump, then that large thing has to be copied to the snapshot before it gets changed.
One serious caveat is that there is an issue between fssnap and real time modules (like xntpd). fssnap will fail if there are any running. So you will need to stop them before taking the snapshot, and then restart them after the snapshot is taken. You don't need to keep them off during the ufsdump. It is only during the moment of taking the snapshot.
Although it is slightly complex and not exactly to your point, there is a wrapper I wrote for Amanda backups so that I could use fssnap with ufsdump in my Solaris backups with Amanda:
http://wiki.zmanda.com/index.php/Bac...yk.27s_Example. There are a number of details on this spelled out in the writeup there.
There is also a "cold mirror" script (user submitted) on Sun's Bigadmin site that I've used in the past. If you have a system with 2 identical drives and want to mirror them, you can use that script. It could probably use some updating. But it also probably works. Just now I wasn't able to find it again, but I'll post it in a separate reply.