As for Hilltop Hanover: the current boundary seems like it would definitely fall under leisure=nature_reserve, since it is natural. If the boundary were to be changed to extend across the street and include the farm section, it would admittedly feel strange to call the whole thing a nature reserve. I would be interested in having the community improve the tagging scheme here.

As for Onatru Park and Preserve: this seems to fit the "front of park"/"back of park" scheme that was discussed in the Cranberry Lake changeset. If we were to follow that, then the area with the sports fields would get leisure=park, but the outer boundary would still be boundary=protected_area perhaps with leisure=nature_reserve. Again, using leisure=nature_reserve on the outside here does feel a little weird to me, but that seems to be the usual tagging at the moment.