No, you will not sign an NLI as a walk-on. Walk-on athletes are non-scholarship team members so an NLI is not required. An NLI is only considered valid when it is accompanied by a financial aid award letter issued from the school. So walk on athletes will not sign an NLI.
An athletic scholarship is a year-by-year contract which means a walk-on athlete could possibly earn a scholarship after their first year on the team. Walk on roster spots provide a great opportunity to many high school athletes who may not qualify for a scholarship or who attend a school that doesn’t have athletic scholarships available. So make sure you consider all your options as opportunities; just because you aren’t signing an NLI doesn’t mean that you shouldn’t join the team.