According to the Wiki it works with 2-H weapons so it should work with bows. I will go try it. http://elderscrolls.wikia.com/wiki/Block_%28Skyrim%29
Edit: No, it doesn't seem to work. To disarm with a shield, you hold down LT, then you hold down RT. However, to bash with a bow, it doesn't matter if you hold LT or press it, the bash is the same; and if you use RT you just ready an arrow. I bashed some Draugr about 50 times and didn't get a disarm with a bow, but with a shield I can get one quite quickly.