Though I've seen no specific mention anywhere, I'd be surprised if it weren't. Vista Service Pack 2 is really not much more than a roll-up of the current patches for Vista, so I really don't expect OneCare to experience any significant issues with it, though there could be less common issues due to drivers or other software on systems from specific manufacturers.
I nearly installed it on a family PC with OneCare last weekend, but ran out of time. I've already got SP2 installed on my own laptop and have been using the Vista SP2 Beta/RC versions there for months without issue, but unfortunately I don't use OneCare on that PC.
In general, if you don't like to experiment and aren't skilled at backing out a problem install, you'd probably be better off to wait until they actually begin to push the Vista SP2 installation with Automatic Updates sometime in June. For now it's just an optional (Important?) install and until OneCare begins to nag (go Yellow) it's really not going to matter anyway, especially since you'll really gain nothing other than some BlueTooth 2,1, WiFi and Windows Search 4.0 improvements from performing the installation anyway.
Generally, I find that if you have to ask, you probably should wait and let the early adoptors with a technical background like myself take the first crack at it. If you aren't hearing much negative about it in a couple weeks, than you could still perform the update manually before the automatic push begins if you prefer to avoid it occuring at a time that's inconvenient for you. Even I will wait for a weekend or evening when I'd have the time available to back out the installation if something goes badly, and I've got 30+ years computer and 20+ years networking/security experience.
