I have snacked on wild northern catalpa flowers of Virginia for years, with no ill effects, and find them a delightful, lovely, fragrant, wild snack, and fresh addition to omelets & salads. I like the faint honeysuckle & sweet pea like flavor & scent. When they dry softly to a honey color, they are like fluffy toasted raisins. Someone said she thought they had a slightly bitter under-taste, but I and others don't, so that might be the particular tree, another variety, or air pollution.
Over the past weeks I collected almost 2 pounds of dried blossoms from my trampoline each morning, and what don't go in my oatmeal, I have put in several containers in the freezer for later.
I'm surprised that I can find very little literature on their food value, but no explicit proscriptions.
I can imagine that a lot the soft tissue of the blossoms might interfere with proper gizzard function (they can also make a sidewalk slippery), but I do see chickens eating flowers & greens, but not a lot of them, and usually when there is plenty of water available.