There's information on August door locks, as well as a couple of other 3rd party devices that work with the Andriod version of the app here:
http://customer.xfinity.com/help-and-support/home-control/connecting-works-with-xfinity-home-device
Looks like for now at least, these devices aren't integrated into the Touchscreen or X1 Home App, and the iOS app support is coming soon.
For what it's worth, I have the Kwikset Smartcode lock and love it - for some reason, I just love the idea of being able to lock and unlock my door with my X1 remote control. :
I also have an automated rule set up to lock the door and turn off my lights if the front door closes after a certain time of night... sure, I could just turn the knob to lock the door and flip a few light switches, but that's not nearly as fun... 