It is best to use the Control-M/Server backup utility ctmdbbck to backup the postgresql databases. There are two modes of backup. A hot backup provides restore to the point of failure (not to the time of backup - basically a restore will restore the point of time of the last hot backup then apply archive logs to get to the point of failure). A cold backup provides restore to a point in time, however you cannot do a cold backup of the PostgreSQL database unless the database is down and you don't want to have to do this on your Production Control-M/Server regularly.
Look up the Utility guide for more information on ctmdbbck.
To run hot backups, you need to set the archive mode. Look up the Control- Administrator guide for more information on archive mode.
I would run a hot backup daily (there is no point in running it any more regularly other than to make restores super-quick) and would also ftp the backup files to a separate location after each backup.