I reckon it would be ok to hose down a playfield as long as you let it dry out completely in the sun afterwards & don't use detergents etc- not that I would try it myself though. Sure would make cleaning easier & I don't think the moisture would have enough time to cause rust or corrosion

Where i've worked we used to wash PCBs quite regularly and as long as you let them dry completely there were no issues

It's not rust or corrosion I would be worried about really, it would be the swollen timber, delaminating ply and eventual planking/cracking of the playfield surface that would be inevitable after such a soaking!

At a guess, playfields are NOT made with marine ply!

Cheers
Jacob