I do this - the key is to exclude the directories / file systems as needed. Otherwise you are doubling the data you are backing up, which may or may not be what you want (depending on how large it is, you may not care)
What I do is:
In the install directory on the client, you will need to create files in a format of "exclude_list.policy.schedule" ( the schedule is optional)
So if policyA backs up OS files, and policyB backs up data files, you would create exclude_list.policyA and list the data directories in it, and create exclude_list.policyB and list the OS directories.
For example - my oracle database servers - I do not want to back up the Oracle db files when I do the OS backup, so I exclude them from the OS backup.
Here is my exlude file for the MSGDR database: ( I exclude the MSGDR data, the GG files and the archive logs )
# cat exclude_list.UNIX.OS_MSGDR.PROD
These are backed up when I run my oracle script ( I call a user backup at the end of the rman script to back up the local oracle file data and control file )