my understanding is that no you cant as it contains lots of 'nasty' compounds from the chemicals in the coal originally. sulphur compounds being the most common.
i know that soot from a coal chimney needs to be weathered for at least 6 months before it can be used.

Only thing I know it is useful in the garden for is to pile it around plants like Delphiniums to keep slugs away when they are emerging, but you need to remove it after a few months.