Are snapshots always consistent?

I'm somewhat confused about snapshots.

Are snapshots (e.g. created with dump -L) supposed to
be always in a consistent state?

What happens if a snapshot is taken, while background
fsck is fixing a filesystem?

If snapshots are not always consistent, how can one
be sure about dump -L output? Is it better to take
a snapshot first, fsck it, and _then_ dump the
snapshot without -L (how?)?

Thanks,

-Farid.

-- 
Farid Hajji -- Unix Systems and Network Management.
http://www.farid-hajji.net/address.html
Quoth the Raven, "Nevermore." --Edgar Allan Poe.