We have several large Oak trees in one of our goat paddocks and our Spanish goats and commercial meat goat herd will stand under the trees and wait for the acorns to hit the ground and rush over to get them fresh off the tree. Oak leaves and acorns are high in Tannins which has been proven scientifically to reduce worm loads in goats. Too much of a good thing is not good for them in the case of tannin but goats are good at being browsers and are a bit ADHD about their diet and get bored eating the same foodstuff all the time and prefer a variety in their dietary intake. As long as your goats have a variety of food sources like feed and browse and pasture, they should be okay because the other foodstuffs they eat will "dilute" the tannins a bit. Acorns are bad for cattle because their digestive systems are slightly different from a goat and their system handles the tannins differently. When we raised beef cattle and the fall rolled around, we fenced off the cattle from the woodland because if they ate acorns, it would dry their milk up and we would have to bottle feed calves.
I am with Goatboy on this one. Oak leaves and acorns are good for them as long as it does not make up the bulk of their diet. Mine wander the woods and eat them but hey also eat a lot of other stuff. The only leaves I know of they will kill them outright are wilted cherry leaves or rhododendron.