I haven't tried it but it seems to me that the results might not be what you'd expect, since the VV technology already involves extra ferrous elements in the pickup. Not sure though, maybe one of the experts can advise us.
I added a steel baseplate to a Fralin Woodstock '69 at the bridge on one of my Strats and the result was fairly subtle, noticeable mostly in the mids though I believe the highs are a bit warmer also. The pickup still has sparkle. The plate didn't add as much extra richness or punch as I'd hoped.