ND is very clear that it is harder to be accepted at the REA stage than RD. They really only want to see above average applicants at that stage. They want to make most of their decisions at the RD stage. MIT and Georgetown (both EA not ED) are similar.
Probably not true that you could get accepted RD at ND but rejected EA. ND accepts about 25% of its REA applicants and defers another 25%.
If you are in the bottom half of the REA applicant pool, you probably are not likely to wind up in the top 19% of the overall applicant pool. Georgetown automatically defers EVERY EA application over to RD. ND (which makes more sense to me) goes ahead and makes more final decisions at the EA stage.
Also, the way that ND’s REA rules intersect with the other school rules means that ND REA prevents applying anywhere else SCEA or ED.