I disagree with the notion that the prospect is a strictly AAAA-type. He seems more like a solid 4th short man out of the bullpen if he improves some (which, of course, we can't know without projections or a history of progression to look at). If he improves more than just some he might be SuA/Closer quality. I know his GB/FB is 0, but with 2 nasty pitches, I would think he would not give up a crazy # of HR. And his high velocity will yield a ton of Ks.
In principle, trading for a career minor leaguer in a salary dump is just like buying/selling players, but the RP he's getting is at minimum a marginal ML prospect, maybe better. So this doesn't really fall into that category for me.