I keep seeing how Hoffman has been pretty good the first time through the order, and he has been ok this season (.662 OPS against), but that's not what he would be doing as a reliever. Unless he's pitching just in long relief, where he may go 2-3 innings, it's more likely it's going to be based on number of pitches.
If you look at his pitch count numbers, relieving makes much less sense:
1-25 .794
26-50 .543
51-75 1.064
Getting through that first inning of relieving is going to be the issue.