The database only contains a small subset of the information in the catalogs. You should backup both the catalog and the database as part of your regular backups of the server if you intend to be able to disaster-recover Backup Exec itself. It can be handy to have the catalogs in a disaster recovery scenario if you don't want to have to catalog other medias to find the right tape to restore.
You don't necessarily have to backup the catalogs to tape, but they're handy to have in a disaster scenario. I copy them to other servers in some Customer sites. In others, I just cover them with the regular tape backup. It depends how big they are and what your tape free space / backup window time is like.
An aside on catalogs: You should always keep an offline log of the most recent tape that contains the catalogs so that, in the event of a disaster, you don't have to waste time cataloging tapes in order to find the tape with the catalogs on it to allow you to determine which tapes you need to restore from. Of course, if you're small enough that everything is ending up on a single tape then that's probably all irrelevant. With an autoloader, though, it's easy to not know what tapes are being used for which jobs and, ultimately, you can end up wasting a lot of time in a disaster recovery scenario cataloging tapes just to figure out which tapes you need to use to perform a restore.
I'm concerned that your catalogs have gotten so large. I mean, that's astoundingly large. I'm sitting in front of a box w/ 12 months of daily backup catalogs sitting at under 500MB of total file size.
I wonder if your catalog retention period is set to an exceedingly long period, regular catalog pruning operations aren't taking place, or something has gone crazy. I'd have a look at the catalog settings in the Options menu, under "Settings" and "Catalog", and see what the retention period looks like. Do you see any odd "alerts" re: catalogs?
It's perfectly safe to turn down the retention period but, as joeqwerty says, in the event that you need to lnow what's on a tape that's aged out of the on-disk catalogs you'll have to catalog the tape to see what's on it.