Last year the cut line was at 60. The NCAA gives any conference with a player ranked in the Top 125 one automatic qualifier to the field, so a few of the low end conferences will get a player outside the Top 60 in, which is why they don't take the Top 64.
There are several keys to making the NCAA field if you're a player in the 4-6 range.
1) Whip some serious tale in the fall. The fall tournaments are the best shot to rack up some wins against guys that will play at 1 and 2 during the spring. A decent fall season can carry you into the singles tournament.
2) If you cross paths with a ranked player in a dual match, WIN. If a player is playing 4-6, they will rarely get a chance to put a good win on the board in a dual match. When the odd chance comes along, you have to make the most of it. This weekend is a good example, although you've got to avoid the dreaded DNF.
3) Root hard for any player you've beaten. You need the players you've beaten to win throughout the year and stay highly ranked to give you a boost. If one of the players you beat in the fall when he was ranked say, #10 suddenly goes plummeting down the rankings thanks to a string of losses, he's taking you with him.
Last year, Virginia put four players in the NCAA field, but Jenkins and Courtney barely made it. They were playing at 3 and 4 last year, but they are at 4 and 5 right now, so it'll be even harder to stay in the Top 60 this year, but I think it is possible. Oddly, I think Courtney has the better shot, because he has wins over Blaz Rola and Guillermo Gomez. Jenkins' best win is over Gonzalo Escobar. I think Virginia is a lock for three participants, a good shot at 4, and 5 is not completely out of the question. This weekend will sort out of a lot things.