JT, here are some thoughts based on our experience:
1. The quality of play at DIII covers a very wide spectrum. Make sure your son knows the quality of play at the schools he is considering and is realistic about how he fits.
2. Our son's former Coach firmly believes in summer leagues. From the very first conversations we had with him, he was talking about not only how he saw our son fitting with his program but also the expectations on where he would be placed in summer leagues. He does this with many recruits that he feels strongly can contribute to the program.
3. DIII coaches often are disappointed by top recruits going elsewhere, even after the student has placed a deposit. It really is true they cannot feel comfortable until the very first day of school.
4. Top DIII programs/coaches recruit very hard. Many are at showcases/area codes, etc. They know the players in advance. Anticipating a player can walk on sight unseen at one of these programs is pretty unrealistic, IMO.
5. Make sure your son visits and spends a weekend on campus with the team and coaches. It is at your expense but very well worth the expense. If the coach really wants your son, he will make this a priority.
6. Ask and understand how the coach views your son in the program. Research the number of returning players but realize that at DIII there is quite a bit of attrition. Our experience was each freshman class had 12-15 players. About 5, on average, were still playing 4 years later. Reasons include injury, academics, lose desire, realize DIII is a lot more effort/time committment than anticipated, family situations, finances. While this is a benefit to the player, it is also why DIII programs might be viewed as "overrecruiting".
7. If the school is considered to be a top academic/athletic DIII, you can anticipate a higher yield ratio for acceptances and more walk ons. Just a fact of life but Fall ball/lifting/etc has a pretty immediate impact on the numbers.