MKbaseballdad,
The process you are describing is called a "pre-read". This is a normal process for recruited athletes. It sounds like Admissions is telling the Coach that it is "likely" your son would be admitted. That "likely" is typical language and there are no guarantees. It is up to the Coach to pass that "likley" information along to your son. Again, this is typical so congrats on the good news.
If you are unclear on anything in this process I would call the Coach to answer these questions just to be absolutely sure of next steps. If you already know your son wants to attend the school, will be supported by the coach and likely admitted then that is pretty much the bulk of it from the baseball standpoint. Have you talked to the Financial Aid dept? If you haven't, you probably should.
Good luck!