Nothing is ever guaranteed. Could be a great situation or could be a nightmare. It will all depend on what they think "after" your son is on campus. What if "after" he is on campus, they tell him, "I guarantee you will never play here". Would your son want to stay there after hearing that? Or what happens If they tell your son they think he needs to go to a certain JC so that he can develop his skills.
I'm not trying to put a damper on this, it could work out great. Every school has some walk-ons. But the only sure thing about baseball is that there are no sure things. If you feel the coach/recruiter is someone you can trust and he is being totally honest, go for it. But always know that people can and do change their mind. Truth is, it is all up to your son and his confidence in proving himself to the coaching staff. There are student/athletes with good scholarships that get asked to transfer... Told they will never play at the college. No one wants to stay where they are no longer wanted.