Welcome to the HSBBW!
I am not understanding your question, but do not think that working with a manager with a milb team will necessarily open doors for your son. Besides he is only 14.
However, there are some considerations to that thought, one of son's coaches in HS, his brother was the former scouting director (still in organization) for the STL Cardinals. He came frequently to watch our games. That coach of son's was also an associate scout for STL. The scout who watched son through HS and called a few days before his first draft to discuss $$, has been involved with the Cardinal organization (he was just with another team for a few years prior to coming back to STL as the roving hitting instructor) for many, many years. Son's agent was drafted by STL also. Do I think that this all had something to do with who drafted him? Maybe, but hopefully by his own merits, not who he knew. Strange as it is, son NEVER met or talked with the area scout from South Carolina. Son was not drafted out of HS, but college, so it is apparent at that time it wasn't relevant but maybe later on.
They may have some connections but they are not scouts, they may make a suggestion to watch yur son play, but don't take this as a substitute for being seen by as many as you can during HS. Besides, that manager may not be a manager when your son is ready for the draft.
Your son's level of talent will be what gets him noticed.