This is a default Reaper setting that I wasn't aware of, and it make a big difference in drum tracks. DKFK/EZDrummer has a humanize option, but everything that I programmed in myself after the fact (any added hits, etc) would have the same velocity.
The quick and dirty way to randomize all your hits so that your drums sound less machine-like is to glue your final drum track together (if it's not already), then open it with Reaper's MIDI editor.
Then Edit -> Humanize, and pick your settings.
And Reaper will do the rest.
Joy! Saved for future use! (I always also program dfh by hand)