What is a good way to imitate that purely with midi and samples?
well, one way is to just get a recording (sample) of someone actually playing that. but the problem there is, it's not very 'playable' for you because you won't have good control over when the final attack is. so if you want something usable, you'll want a steady sample of a continuous drum roll, with fast attack and fast release, so it starts and stops immediately when you press or lift the key, and then you'll want a separate sample, on another key, for a normal snare hit. and then you can play both keys to time the ruffs any way you want. And of course, for decent results, you'll want to make them both dynamic sensitive, and have many different versions of the sample, for different loudness levels, and also many different versions for the same loudness level, so they don't all sound identical