I have a DSC alarm panel and an Envisalink 4. When I hold the door icon (I think it’s called Exit on some keypads) the garage door will open. Essentially it’s setup as a momentary relay connected to my garage door opener.
That is an interesting use of the exit button, I guess the button on your keypad was reprogrammed to do something different, most likely one of the command output functions which are *71 and *72 + code if required.
As per the integration doc you can use the alarm_keypress service, try sending those codes and see if that works…