Ok, we'll here's the deal... Can you put one on? Yes. But.... With a surface signaling device like a dive alert - you have to hold it above the water to have it signal. Attached to your waist - this would not be possible. So what you would do is have to unhook the inflator hose from the air trim (which the dive alert could already be on) and then hold it up above the water line. Now the BC's with the air trim system have a way to route the hose through the bc, and if you do that, again, you would probably not be able to get it up high enough out of the water to function - so I would say you have 2 options. 1 is don't route the hose through the bc, leave it on the outside with the dive alert hooked up, then unclip, hold it up and hit the button when you need it at the surface. You will already be inflated, and won't really need to hook it back up - so that would work out fine.
or 2, the other option, and an option I have used for several different uses in my diving, is run an extra inflator hose. They are only about $19 - and you should have plenty of spare ports (unless diving dry) and velcro the extra hose somewhere, pull it off when you want to use it. This way you can also carry one of those rubber filler type things for air lift bags or whatever...
Hopefully that makes sense!
or 2, the other option, and an option I have used for several different uses in my diving, is run an extra inflator hose. They are only about $19 - and you should have plenty of spare ports (unless diving dry) and velcro the extra hose somewhere, pull it off when you want to use it. This way you can also carry one of those rubber filler type things for air lift bags or whatever...
Hopefully that makes sense!