I'm currently "backing up" my linode by dumping off the mysql database, and compressing that + the www/ filesystem where the web pages are served, and scp'ing that to another linode in another datacenter.

It works, I know I can restore the site and get it up and running, but I'd like to use Linode backup instead (turnkey, etc).

My fear is that as it sits, if a datacenter goes sideways, I am toast.

Any way to move a backup around?

Once a backup is in the Linode Backup service no. You could sync the MySQL dump to another Linode and have the backup service on both Linodes. Then it gets backed up in both datacenters.