I believe it makes very little sense to go and add wheelchair attributes to these grass-for-unleashed-dogs parks without knowing exactly what we're doing and why.

Especially since a dog is allowed to play here without a person needing to step on the grass, which means we get into questions about defining what 'using' this amenity even means.

Looking at https://wiki.openstreetmap.org/wiki/Key:wheelchair I would say it's safe to ignore the accessibility question?

We can't positively state it's a wheelchair=yes or =designated accessible place, because there's A. no sign and B. no one with a wheelchair told us to mark it as such.

At the same time, I'd pose it's also not true to mark these as wheelchair=limited or =no without further guidance. 

PS: doing something here would also only make sense if we apply attribute changes to all dog_park amenities across at least the city, if not the country.