The UFC has really cracked down on vaseline usage, and if I'm not mistaken, it can now only be "administered" by the commission's specified Cutmen.
Anderson Silva has a real
famous clip of him greasing up during a UFC 97 fight, that is FAR more obvious, than the clip of GSP with Phil Nurse. Personally, I think that while it is a small advantage to be greased-up, it's not as big of one as people think it is.
In the Penn vs. St. Pierre II fight, GSP absolutely abused him, and I don't recall him ever being in any type of
true submission danger, where extra "vas" would have benefitted him. I mean he literally annihilated Penn from top-to-bottom, and won when Penn was unable to answer the bell for R5. I distinctly remember this win by GSP because in the pre-fight hype shows, it was Penn who was accusing GSP of being a "quitter" in his fights, and I thought the way it ended was particularly ironic.