As far as I know there is no easy way to extract just policies from this backup.
This backup you mention seems to be a ssgbackup
Which has 2 options ssgrestore/ssgmigrate
Migrate System Data - CA API Gateway - 9.2 - CA Technologies Documentation
ssgrestore intended for restoring to the same system in case something went corrupt.
ssgmigrate intended to migrate the data to a new system.
This should have all the files needed to bring up a similar image to the machine that is/was gone and have access to the policies. But this is in the form of a mysql backup main_backup.sql.
If you provision a box and do the ssgmigrate then you can use one of the standard migration tools to move only policies for example gmu.
Get Started and Run GMU - CA API Gateway - 9.2 - CA Technologies Documentation
GMU which is intended to take policies and dependencies from one box to another. Or of course just the traditional Policy Manager export/import. Or restman and there are some other possible choices for policy migration.
I don't think it would be wise though just to try and append data from 1 table in that sql backup into the existing systems table(s).
So my suggestion would be if this is required to restore the image and then use one of the traditional methods of migrating data.
Thanks.