Bad experience Lancaster KOA

In matter of fact the ADA compels reasonable accommodation and access not only on employers but also for the public at large in all businesses.

Again, "reasonable accommodation" covers employment, public accommodations are a bit different. From the Department of Justice ADA page:

Public accommodations must --
Provide goods and services in an integrated setting, unless separate or different measures are necessary to ensure equal opportunity.

Eliminate unnecessary eligibility standards or rules that deny individuals with disabilities an equal opportunity to enjoy the goods and services of a place of public accommodation.

Make reasonable modifications in policies, practices, and procedures that deny equal access to individuals with disabilities, unless a fundamental alteration would result in the nature of the goods and services provided.

Furnish auxiliary aids when necessary to ensure effective communication, unless an undue burden or fundamental alteration would result.

Remove architectural and structural communication barriers in existing facilities where readily achievable.

Provide readily achievable alternative measures when removal of barriers is not readily achievable.

Provide equivalent transportation services and purchase accessible vehicles in certain circumstances.

Maintain accessible features of facilities and equipment.

Design and construct new facilities and, when undertaking alterations, alter existing facilities in accordance with the Americans with Disabilities Act Accessibility Guidelines issued by the Architectural and Transportation Barriers Compliance Board and incorporated in the final Department of Justice title III regulation.

A public accommodation is not required to provide personal devices such as wheelchairs; individually prescribed devices (e.g., prescription eyeglasses or hearing aids); or services of a personal nature including assistance in eating, toileting, or dressing.

Just as a public accommodation isn't required to provide wheelchairs, they are probably not going to be required to provide a shuttle service when that is apparently not needed to access the campground, but just to most easily leave the campground without the camper's guests having to pay the uniformly imposed guest fee. Now that's not to say that the campground is following best practices - imposing a guest fee on those just picking up campers for off premises activity is a bit over the top, although I can understand campgrounds not wanting to police this. The overall attitude of the ownership may be more of a problem than the specific action here, which probably isn't an ADA violation unless the law is interpreted more expansively than is presently the case.