Yes, I currently don't check if you place the orb directly on a tree. That leniency lets you do things like having ornaments hang off the tree, which would not be possible if I went with a pixel map.
I count on everyone to place ornaments properly. Since you can remove your own ornaments and place them again, you can fix things. In case of the contrary, moderators are able to remove ornaments, and have been instructed to do so for any that are placed in mid-air.
