Ext3 users - Nov 2010 - corrupted quotas/running quotacheck on a mounted filesystem

Hi,

1TB ext3 volume mounted via iSCSI on a RHEL5.5 system

the quotas on one of my systems (with ~5k users) seems to have become out 
of sync with reality (500MB reported, but 100G+ in reality) - i'm seeing 
some odd behavior when running the quota 
tools also. For example, "quota -u" shows no quota for some users, but
when running "edquota", they're visible in the list.

As such, I think i'm in need to running the quotacheck utility. From the 
man page, it would appear that this is to be run on an unmounted 
filesystem - is this accurate? can it be safely run on a mounted 
filesystem? I understand that the results might not be completely accurate 
if information changes during the quotacheck run, but it should be more 
accurate than it is now!

I'm not really able to take the system offline for an unmounted filesystem 
for another month or so, but would really like to get some more accurate 
figures in the quota.

Or is there another option i've missed?

Thanks,

Matthew