A few D3s do give likely letters, but, as noted, it's not a guarantee. This is why the whole thing is so complicated to understand.
D3 schools have no roster limits. And "high academic," even if you start with an average SAT score of, say, 1250, covers a very wide range in terms of admissions percentages; anywhere from 7% to 50+%. (Chapman, who just won the D3 World Series, goes to Headfirst). Some D3 coaches (at all levels of selectivity) keep their rosters at 30-35; some (again at all levels) will put 50+ kids on the roster (although most don't play much, or get cut, or they have a jv team, or something). Some D3 HAs have fixed numbers of slots/likely letters, some have "tips" or can put a player on a list they give to admissions, some have no influence. Does your player want to be an active player, or have a shot at sitting on the bench? Do you want academic merit money?
So, at every school, you have to ask the exact very specific questions that you are asking here, and ask exactly how their admissions works, and then try to figure it out, before the Early Decision deadline. It will make you crazy. The only upside is that the HA D3 coaches themselves know all this, and are playing with the same variables as the recruits.