Yes, it is possible, we have implemented it at our customer datacenter using an HP R5000 UPS with the additional HP network module
which supports ESXi 5.1.
I'm guessing you did it for ESX < 5.0.
The service console goes away in ESXi 5.0, and as far as I can tell so does the ability for HP to gracefully shut down ESXi.
The URL you gave shows their software supports only up to 4.1, and their installation instructions depend on a service console.
Anyway, borrowing from the Schneider Electric slides on how to get an APC UPS to shutdown VMs I think a suitable solution can be put together.
It looks like you:
1) Install vMA 5.1.0.1 as a VM.
It's SLES11 or OpenSuse11, I haven't looked at which.
2) Install HP Power Management Agent for Linux into the vMA.
3) Use the skeleton script that is installed in 2), plus the slides, to create one grouping of VMs that you can run a command on.
Then, script a multi-VM shutdown command.
If you really go and implement this, then what I'm thinking is set a 2 minute delay on the UPS before it sends out a shutdown alert.
It's more work otherwise if you have to start a countdown in your script, then abort the countdown if power comes back.