I've used it on a previous car, a Ford Taurus, with no ill effects. That was added through a vacuum line though, not used for oil sludge.
I believe I've seen people on bobistheoilguy.com recommend doing a couple of real short oil change intervals with Pennzoil and a good oil filter (not the orange Fram) to clean out sludge before. That would be a safe bet. I'm going off of memory though. Throw this into google and see what you find:
site:bobistheoilguy.com clean oil sludge