During the season, Jeff Niemann began throwing a splitter (as documented elsewhere), but during his final appearance of the 2009 season, he also began throwing a cutter. The Brooks Baseball pitchfx page is here and no cutters are actually recorded. Look at the slider average and max velocities however. Some pitchers do throw sliders in upwards of 90 miles per hour - David Price and Felix Hernandez for two - but we have seasonal data on Niemann that suggests his slider sits in the low-80s.
Even more, look at the comparison of velocity and movement between NIemann's "slider" in that game and the one that Lance Cormier throws. Believe it or not, Niemann did not pick this pitch up from Cormier, or James Shields, or anyone else. He just gripped the ball with what amounts to his cutter grip and felt comfortable throwing it during pre-game warm-ups. Eventually he felt comfortable enough to use it during games, and gave the Yankees a cutter-heavy diet that saw a few whiffs - something uncommon when it comes to Niemann's collection of fastballs.
Unfortunately this is the only game where he unleashed it, and the sample size is so ridiculously small that to say whether it will be a worthwhile pitch or not. There's a very good chance Niemann is a better pitcher when it comes to processes this season, but worse when it comes to results. Only time will tell if the cutter and splitter contribute.