so long as the bulbs have enough soil over them to protect them from squizzers ,freezing etc etc and the bark is not too deep(less than a foot or so at a guess)or toxic should be much the same as planting them in grass/bare soil.
my local park has a mass of them under some fancy birch trees,they are in soil but it get very compacted once the leaves have died back and i have seen them doing well under the edges of a gravel drive so i recon they can push through bark no prob.