The big advantage of having the UPS management card instruct the ESX servers to shutdown is that there is no single point of failure in this (other than the UPS itself). By using the vMA or whatever software in between, it means that there won't be any graceful shutdown if that management piece is unavailable. Sure it runs virtual but even then...
By going to ESXi (even with vSphere 5) we are putting some steps backwards in terms of UPS usage. VMware seems te live in a world where there are no UPS'es but our customers use them. Our customers demand that VM's are being shutdown gracefully, and also very important, get started automatically after the power outage.
VMware HA doesn't work with this as gracefully shutdowned VM's won't get started up, so you need to use scripts.
To be honest, I wish VMware either kept ESX or pushed/helped the UPS vendors like APC and HP to build good working agents on ESXi.
:smileysad: