Time warp forward to 2018, and I’m still alive, running a Vera Plus under UI7, and just tonight FINALLY plugged in my X10 PLI using the same serial-to-USB setup mentioned way back at the top of the thread.
So far, things are looking promising, having followed all of the steps listed at GitHub - bwssytems/vera-x10-cm11a-controller: A plug in for micasaverde products to controll x10 devices through a CM11a. and using the files downloaded from there.
I’m about to grab a random X10 device from my trusty old collection, dust it off, plug it in within earshot, and try sending it some ON/OFF commands, just like the old days!
If it works (would be the first time I got any Vera to “speak X10” but I’m optimistic), I’ll certainly update this reply with details!
Fingers crossed,
UPDATE 1
Oops, my PLI is not a CM11A, it’s an Insteon 2412s, with a serial cable connected to VeraPlus via a serial-to-USB adapter.
UPDATE 2
I’ve written to Brad, (dev of the X10 plug-in) explaining that the parent Device it created has disappeared from my system, leaving (4) orphaned child Devices named “X10-A1”, “X10-A2”, etc. They don’t do anything (yet).
More UPDATES as I make progress on this experiment… 
UPDATE 3
Good news and bad news. The bad news is I never got the (manually-installed) “CM11A PLI” plug-in to work. I even tried installing the (identical, but installed from the App Market) “X10 CM11” plug-in, but no joy.
So, in desperation, and since I actually do have an Insteon PLM plugged in to Vera Plus, I tried “Add Device+” using the category “Insteon Device”, under which there’s an X10 section (WHO KNEW???).
The good news is that immediately after setting up a new Device set to channel “A” and device number “2” (the appliance module I chose for testing) – and making sure Develop Apps > Serial Port > “Used by…” was set to “Insteon” – I was able to click “On” and “Off” and the module produced its distinctive CLUNK with each command!
SUCCESS! 