I'm not the least bit in favor of "underdrafting" with the 3rd round pick.
First of all, Rodon doesn't need to be offered a dime over slot. He has no leverage, and the Sox can pretty much assure him he will hit the active roster no later than September 1.
Sox can go 5% over their total allotment without losing future picks. That means they can offer Adams money 10-12 slots higher than where they drafted him without having to go underslot on other picks.
Don't waste the third round pick. I'm fine with taking a guy who has 3rd-4th round talent that they are certain will sign for slot or slightly under, but I'm not fine with taking a guy who has 10th-12th round talent and offering him $100K.