I don't think anyone actually states what those are. What makes a "blue chip" athlete can be an ever-changing set of criteria, based on who they have to choose from.
From a pure NCAA Division 1 standpoint, most colleges will be pretty darned interested if you're consistently vaulting 17'-0" or better.
There was a high school junior from Florida who was regularly clearing 17'-6" four years ago, and last March a high schooler from Louisiana (Armand “Mondo” Duplantis) cleared 19'-1". That guy had his pick of colleges, and signed with LSU.
With that said, USNA has a Plebe this year vaulting 16'-0" (at least he did last month) and a 2C (Junior) who vaulted 16'-4 3/4" at the same meet.
It could very well be that neither of them are "blue chip" athletes. They also have a Firstie who vaulted 15'-3", another Plebe who vaulted 15'-3", and another 2C who turned in a 16'-0" tally. Five vaulters on any college team is quite a few (in my opinion), and I would surmise that at least four (if not all of them) are walk-ons. It's just conjecture on my part, though. Whether or not the fact that they are vaulters helped them get an Appointment is anyone's guess, unless you know them and can ask!