I mean, "roles" are not "innings" but clearly in the Cotham/Thomson era they are doing much more sophisticated leverage and match-up stuff. Except, I reckon that once the bullpen gets short, you have no choice but to just use what you have.
Nelson has a 4.57 ERA on the season but a 6.10 ERA in the last 28 days. WHIP - not great to begin with - jumped from 1.410 to 1.548.
Bellatti has been about the same (or even better) over the past month vs. overall but anecdotally it feels like he had a few tougher outings recently (most recently in Arizona and also against the Mets). But all relievers have the odd tough outing, and the whole team had trouble against both those clubs!