if iPhoto came with my Mac, can I still get free updates after Mountain Lion?
Yes! When you open the App Store's Updates tab, you'll see a special dialog allowing you to accept the apps such as iPhoto that were bundled with your computer. If you accept them and enter your account info, the licenses will be automatically associated with your account. In the future you'll be able to receive updates exactly as if you had purchased the apps.

(The details probably depend on which computer you have and when you purchased it. But if your computer is a relatively recent model then you probably will have access to these apps. If you want more details you may need to contact Apple.)