As others have mentioned, it's probably easier for a "walk on" to get a spot on VOST than most other sports. While several positions (helm, navigator, sail trimmers, foredeck) require experience, there are also positions, i.e. "rail weight" that require mostly physical size, strength and some agility.
Inshore, or dinghy, racing can sometimes use an inexperienced person if he/she is the right size to fill out the crew for an experienced helmsperson. Here, it's really important that the person has agility, and can learn rapidly.
As mentioned in a previous post, your Plebe WILL learn sailing basics during Plebe Summer, and it will be possible for him/her to pursue a "skipper's card" for the right to take out the Colgate 26's later in his/her career as a Mid, even if he/she is not on one of the sailing teams.