Hello Matthew,
You are right! That is simply not one of the ASyncOS functionalities. I suppose that's because it's hard to make sure all UPS vendors are supported and.... maybe more important.... since not many enterprises are using this functionality. (As far as I know, correct me if I’m wrong.)
Maybe you can write a script to bring your Ironport(s) down, that is executed form one of you UPS controlled hosts, just before that host is shut's down by an UPS notification.
I must make the remark that shutting down an Ironport before a power outage makes sense. Ironport is also using some DB functionality internally and those DB('s) can be damaged by a hard power off.
Hope this helps.
Steven