Most college rugby in the United States is a club rather than a varsity sport, and walk-ons with experience are generally quite welcome. There are some exceptions amongst schools (like U. Cal. Berkeley or Brigham Young) with stronger programs, but (if interested) you should make yourself known to them. But don't be expecting a full ticket ride of the type that gridiron or basketball players get -- rugby scholarships in the American college system are very few and far between What you really need to do is investigate the sporting programs at the school (or schools) you are interested in and see how their rugby programs are organized.