My understanding is your correct in your suspicion

The DIII midweeks are, in effect, a scrimmage. Like you said, a reward for long-serving players. Matthew McLaughlin, a program veteran without much game action previously served as captain and scored in last year's game. I suspect the main players this year will be similar stories. I kinda like it as a low-action midweek/midseason opportunity, tbh. And I think it's also worth considering that it offers players who will be transferring out of Notre Dame at the season's end (McLaughlin for instance is now at Marquette for his fifth season) a chance to put some game action on tape for coaches they might be talking to later. I think that's a nice thing to offer those players who wouldn't have much film to show prospective coaches otherwise.