Thanks for the questions.
1) The reason Subversion gets more press is because we've supported it for longer. It's not indicative on which one we 'prefer'. Do you have a source control system for your application code? If so, it might make sense to use the same one for the sake of easier administration. Subversion is a more established tool, so its maturity might give you confidence, but if you like the DVCS model of Git and Mercurial, it might be worth considering.
2) is the production database the one you wish to manage via source control? SQL Source Control links to development environments, not to Production. If changes are being made directly to production, you can identify these using SQL Compare, and copy them down to a development environment, and then commit them. As we apply frequent polling to your linked database to detect changes, it would be a mistake to link a production environment to SQL Source Control.
Do let me know if you have any further questions,
Red Gate Software