I have, and it will work to varying degrees based on the specifics of your
setup. The caveats are:

1) domain  A and B cannot have the same name, but not actually be the same domain
(e.g. both called contoso, but created at different times and not synched).
2) Everything should work without modification if there is a trust relationship
between the domains.
3) If there is not a trust relationship, you'll lose all personalizations and
you'll have to manually fix the users  and permissions.

My only concern here is when I do run the restore  and the portal is up and
running on the new domain, how do I get into the portal since none of the
original users  no longer exists? Do I set this site in IIS as anonymous?

The administrators of the box have full access to the Portal Sites so
you can go into the restored database and change the permissions.