I would think any "nut" tree would be suitable for smoking. I did a Google search and found that almost every part of the hazelnut or filbert tree has been medicinally used in one way or the other. I only found one reference specific to "hazelnut" for smoking from this link:
http://www.kxl.com/arDisplay.asp?ID=31887&SecID=13 Ouoting from the link above: "It�s better to have a little wood smoke than too much. Keep this in mind when using more pungent woods like Hickory, Pecan, Oak, Hazelnut, which can turn meat bitter if you over smoke using these woods."
One link said that 98-99% of US hazelnuts were grown in the Pacific Northwest. Maybe someone from up that way has used hazelnut wood for smoking.
Sounds like it's ok. If it were me, I would use it as I would hickory. My opinion is to give it a shot. Do your own reasearch though. I don't want to be responsible for a bad smoke or a uneasy tummy.
Let us know what you do and how it works out!