That's nasty. Maybe you could automatically inject test data into a fake account and run test queries on the backup. That will not verify you are getting everything but at least that you got something recent.
That's the thing with backups, they can fail or become corrupt in many ways. If you don't use them for something on a regular basis or have some regular verification process you may not know what you have until it's too late.
And, of course, I've also seen situations where subtle data corruption in the master database leads to weeks of subtly corrupt backups. By the time the corruption was discovered we faced the choice of rolling back several weeks to the last good backup or fixing the corruption. In the end we had to do a kind of merge -- it was a real pain.
As a baseline, you should at least restore from your backups occasionally.
It helps that I'm familiar with the data -- so after restoring the backup I expect to see games, messages, forum posts, etc that I've just seen in production.
I do some more thorough automated tests on the backups less frequently. App specific things, like replay games and verify results, etc. This process is more about assuring backward compatibility with the code though.
I think verification should ultimately be somewhat app specific. That said, I'm sure you can find tools to help with verification.