NoFo - Deer will browse the Washington hawthorn, but only the new shoot tips that have no thorns. The thorns are about 2" long when the needles " mature ". I've never seen Washington hawthorn with berries other than red in color. I can't speak to green or yellow fruit - never even heard of those colors of fruit. The berries that drop will sprout new trees easily and give you a thicker patch of W. H. - or free seedlings to transplant elsewhere. Grouse and turkeys love the fruit, and deer will lightly browse it, bed in it, and make scrapes under the older trees. Our deer seem to like to pass thru our thicket on the way out to our food plots, for whatever reason. No disease or bug problems for us. One of our young ( 8 ft. ) perimeter trees got pulled over accidently by a PTO mower deck. It pushed up vertical growth and formed a " wall " of hawthorn. In the fall / winter, we flush grouse out of that thicket regularly.
IMO - not a thicket you want to walk through or drive an atv through, which is why deer and grouse love them. No disturbance !! They are a GREAT critter / habitat tree, not people-strolling material.
We have a thicket of 10 older trees, planted 20 years ago, that are about 15 ft. tall - and numerous " free " seedlings growing in / around them. Also have several single trees planted around the property - mainly for grouse / turkey food. If you have large acreage, a large thicket would make EXCELLENT bedding / security cover.