IMO, it's a better idea to keep a dedicated alarm system that does what it does best (protect your house) and then just interface it with Vera. This way you have the reliability of a proven alarm system, but can still use information from the alarm system to inform the home automation.
The Safewatch Pro 3000 is basically a Ademco Vista 20p, only (and I may be wrong about this) with a few minor features disabled. As a result you can use the AD2USB device to interface with it. I've been doing this for years and have loved it. The AD2USB mimics a keypad so it has all the information and functionality one would get with a keypad. You can get alarm status, enable/disable the alarm, and get instant status information on the status of all your zones.
Personally I use my Safewatch Pro 3000 in this way, and it is really the basis of almost all the triggers for my house. When I leave we arm it away and it automatically makes sure all doors are locked, lights are off, and thermostats are set to "out of house" temperatures. When we get home and disable the alarm, lights turn on, thermostat go to normal temperatures, etc. Arming it to "Stay" does similar things knowing that we are in the house.