regarding your first part - if you redshirt him or if you start him some games but not enough to meet his "minimum" you will hear about it, his WE will drop and he will most likely transfer. Your reputation will also take a hit. To avoid that, you must start him between 70-90% (seems to vary by kid).
As to whether you should have taken walkon instead, if you plan to break the promise and the kid transfers, then yes, as this way will hurt rep a bit while taking a walkon wouldn't. If you can suck it up and meet the promise and the kid develops into something (you had to have recruited him for some reason, right?) then you are better with the player.