If your OpenERP server is a Linux server, then here is a link to some beta bash scripts that may accomplish the backup portion.
https://github.com/nagalman/oerp-admin.sh
Please note these scripts are released under the GNU GPL. If you improve them, please share the changes with me and others.
As far as doing a hot backup, a true "hot" backup is not possible with atomized databases (like PostgreSQL). You can dump the database to a dump file, then backup the dump file. While Postgre is dumping the database, no operations can be performed, so its best to do a database dump when OpenERP is not being used (ie 4am Sunday morning). If you set up a slave PostgreSQL server, then the slave server may be able to be dumped, but I do not know this for certain. The dump operation takes only a few seconds (of course this depends on the size of your database and the speed of your server, etc).
If you have a master slave(s) setup, you may be able to dump a slave database (slave databases just replicate what is in the master to be able to support fast read operations. Only the master can do add, delete, update) while the master is able devote resources to add, delete, update.
The scripts above are only set up to backup a single or master PostgreSQL database. I haven't done any testing in an environment that has master slave(s).
I haven't experimented with incremental backups of a database dump files. I suppose backup tools like TAR and others could perform this since the database dump file is just a file.
I hope this helps!