This is usually not a deal killer. It just means the Park is non-conforming with current zoning and is grandfathered.
You should speak with the Town Manager or whoever is most knowledgeable on zoning and get a Certificate of Zoning from them which should provide you evidence that the Park is nonconforming today. Also speak with the code enforcement people about your ability to move homes in and out of the Park with the existing setbacks. If the Park has a good reputation and no issues they shouldn't give you any grief. Most towns also have ordinances that will confirm this position on grandfathering or noncomformance (e.g. the usage prior to zoning can be continued unless usage ceases for 18 months).
I have looked at several Parks like this, most of the time everything has checked out and the city been okay with everything and documentation check out - in a few cases the city says that homes cannot be moved in. If this happens to you there are a couple recent threads on how to work this out using a municipal attorney with grandfathering experience to call the City attorney to ensure there is alignment.
In one instance I had my real estate attorney get clarification with a small town's attorney and this subsequently caused them to update their mobile home park ordinances because of their misunderstanding of state law. It was a quick thing and not prohibitive, but it does happen.