Buzz ,
I don't see a problem with this , at least the cabling is monitored , which is better than some efforts on the lift alarms I have seen over the years.
I have just been asked to link in the standard disabled toilet alarms into a system , as security eventually found a lady in distress , and no one heard the standard alarm.
I have also monitored central battery units on emergency lighting systems for fault through the fire system , as it was monitored for fault at the receiving centre.
As far as I know the shutting down of plant via BMS is a no no , and should be hard wired .
The only thing that you might get pulled on is generating a red led on the panel , thats if you are going to do that way , as you know all the other actions could be slow to register ie fault , and the lift button is probably non latching , so it could get messy.