Tested with ExU pipes and TE ducts. When you connect a chest via piping to a coke oven block, whether it is a valid multiblock structure or not, it takes the coal from the chest. This means that if something like Mystcraft borks your ovens and you don't get to it quickly enough, you can say goodbye to your coal inventory.

(It took me a while to figure out that this was happening. Goodbye, 8 stacks of coal. Heh.)