I was hoping someone had a definitive answer. I do use it on clover. I would never have thought to question it's use around trees. But, then I had to think about it. IMOX is a selective contact herbicide that has some soil residual making it effective against germinating plant seeds. The dose makes the poison, but 6 oz - 8 oz isn't a large amount. I've used that rate per acre on established clover with good results. The clover survived and the weeds didn't.
So, a tree is already established. It has a root system and not germinating seeds. Don't spray it, the IMOX, on the tree leaves, although I think the worst thing that would happen would be a leaf-drop with re-generation.
The same would probably be true for any crop production herbicide. If the IMOX label worries you, don't let it. I think it's labeled that way to get around registration and patent considerations attached to some of the other herbicides containing the same active ingredient, but trade-named and labelled for crop production.