Ableton's new Push controller allows one to play only in certain scales, is this something that can be mimic'ed in a drum rack or something else? Are there any VSTs that have this ability?
Live has a "Scale" MIDI device that filters incoming notes and snaps them to the closest "correct" scale note. You can find it under MIDI Effects in the browser.
This won't be as useful in a drum rack, where the contents of individual cells don't necessarily have any association with the note that triggers them, but for any tonal instrument it should work just fine.