I just used Z-Wave security sensors to create my own house alarm in Vera.
Door / Window contact sensors, indoor siren, motion sensors etc. Also used a cheap RFID keypad with fobs and a Fibaro Universal Binary Sensor.
Also have a wall mounted tablet running Home Remote app which can be used to disarm the house with a pin code.
I’m sure there are better dedicated wireless alarm systems out there on the market place, but as you say you’d need a way to be able to integrate it with Vera. If they have a software API you might have a fighting chance or doing something.
Search the forums for possible brands?
As for what you can do with Vera? the skies the limit really. I’ve created scenes and automations for when my “alarm” is tripped.
For example if it’s night turn on all lights inside and outside the house, start LAPD flashing lights on light strips connected to Fibaro RGBW modules, sound the siren, open all curtains and blinds, send a text to my phone via Telegram, call my phone using CallMeBot.
You can do much more than a bog standard traditional alarm if you are prepared to program and code some automations.