I'm not sure about what does and doesn't. Moisture up high can cause bark rot and then tree rot, so I've been told. When leaves drop, they then degrade and don't add up to too much, I think. Also, check out this pdf from Cornell that shows blue berries all mulched up:
http://www.fruit.cornell.edu/berry/ipm/ipmpdfs/bbmulch.pdf
The biggest #1 question with blue berries is: What's your soil pH? If it's above 5.0 (which, unless you live in a bog, most are), then you can blame this. Lots of people try to grow blue berries here and wonder why they don't thrive. Then, when they hear about pH, they try to surface mulch to accommodate the high pH. It doesn't work quite like that because the soil parent material is even a higher pH than the surface soil and that's where the roots reach to. So, the best thing to do is dig up the blue berry, mix in peat moss until you get the right pH (there must be a more
permie way, but this is what I know and do) and then put the blue berry back. THEN mulch yearly with saw dust (I do leaves).
I know, a pain in the ---, but for me it's worth it.