At the resort we visit, non-nudists come in all the time for various purposes. One delivers propane to the resort's many tanks, others drive FedEx or UPS trucks, others include health inspectors and food suppliers for the restaurant and snack bar, building inspectors for new additions, and others. The resort hires bands to play for their dance on 3-day summer weekends, and the band members are not nudists (although one singer did take her clothes off and swim in the pool). Several TV stations have done feature stories at the resort, mostly about the nude church service every Sunday (you can find these on YouTube). First responders are sometimes called for medical emergencies, and they come right in.
I don't know if Postal Service employees ever come in (I don't recall seeing any). Residents have mailboxes outside the front gate, and that's where the mail trucks go. Several kids have lived there over the years, and the school bus likewise picks them up somewhere outside the gate. Wouldn't THAT be an interesting field trip?
The resort and its residents are well-known in the community, and contribute to local charitable causes. The resort brings in a significant amount of money to the area (restaurants, gas, etc.).
Nudists don't care if clothed people see them or not. They sequester themselves to not "offend" non-nudists who might spot them accidently.
Also, many resorts participate in "National Nude Weekend" on the second weekend of July. Non-nudists are welcomed to come and tour the resort while clothed, and try nudism if they like. There are often discounts and special events. You can find out more (including locations) at:
www.aanr.com