As a HS coach, it was certainly part of the job responsibilities to try to help players advance if they wished to do so. The best way to do that over the long haul was to develop relationships with the regional HC's/RC's where possible and maintain a reputation of someone with integrity that would steer both the college and the player in the right direction toward a probable fit. If there was a conversation with a college where the player was most likely not a fit for whatever reason, sometimes it would do no good to tell the player. Sometimes it would. If a player had character concerns and this was a turn-off for the RC, this is obviously a very slippery slope with regards to telling the player about the contact and conversation. I would most likely be inclined to not tell the player of the specific school but instead be up front and tell him that I would be obligated to share with any school who asked about such concerns. This type of general conversation with the player (in advance) has been a helpful tool at times with steering that player toward working out of the character issue.
A coach can't just give glowing reviews for all. That conversation usually includes discussion with some detail around various skill sets and a checklist of pro's and con's, along with character/personality, grades, family, etc..
Most HS coaches have some level of ongoing dialog with their players, at least occasional status checks on their recruiting efforts. One of my sons is a RC for a small school, other side of the country. He recruits California and will occasionally tap into my network of HS coaches by having me make a preliminary inquiry on a player. I have made a handful of those calls in the last few weeks and each coach had at least a decent awareness of the recruiting status and likely direction of the player in question.