But I would definitely communicate the fact that you have a 4 year ROTC scholarship to the admissions department, as it MIGHT help them to know Uncle Sam will be paying full "retail" tuition.
It may be even better if the PMS/PNS is the one who notifies admissions.
Supposedly, no, but actually, yes. It isn't so much that the xROTC unit will plead your case. If they did, then every borderliner would be asking for help and that's not their job.
However, if you have an xROTC scholarship in hand and your admissions package is borderline, the school will take you, carrying your own scholarship, versus the applicant who is looking for financial aid.
If the xROTC unit has a relationship with admissions--which some do-- then all the better.
Unless someone on this forum is on the admissions committee for ND or a member of their AROTC Cadre, I don't believe anyone can answer that. In fact all of this is "speculative" regarding how a scholarship can boost your chances or not. It is not unlike the thousands of "chance me" questions that are posted here.
In my opinion, just take action and optimize your chances! The good thing is that notifying them of having an ROTC scholarship is very unlikely to hurt you and possibly even help you.