Are resident owned manufactured housing parks a form of shared equity homeownership?

They can be.  Resident owned manufactured housing parks are generally organized as cooperatives with each homeowner owning a share in the cooperative corporation which owns the park.  Many of these parks are organized with the specific purpose of preserving affordability of this form of housing.  While it is rare for these cooperatives to impose specific price restrictions on individual homes, they typically limit lot rents to preserve affordability and limit the resale value of co-op shares.  This shared ownership of the land and park infrastructure is generally sufficient to protect ongoing affordability of the housing.