Yes, if you want to backup you SQL databases then you ideally want the SQL Agent, since your database files will always be in use and therefore locked, otherwise you'll need to get SQL itself to produce a backup of the databases, and then you can back those up along with the rest of the servers data, but for disaster recovery less ideal since you would then have to restore each db individually.
You can restore a system to a new machine without the IDR agent, but the benefit of using it is the speed which you can recover the system. Without it you will need to setup the new server with Windows, get all the drivers etc re-installed, get it back to the previous patch level, install Backup Exec or the remote agent (depending on if it's the media server), and only then will you be able to perform the restore.
I should warn you though, I've been trying to get IDR working on one of our new systems without success recently, though that may just be due to the config of our server, so if possible I would definitely recommend if you get the chance, eg the server isn't get in a production environment, do a complete test run of the IDR restore so you're happy that it will work correctly. The last thing you want is to discover your recovery doesn't work properly when your server dies, and to restore it manually.
