A good way to roast hazelnuts

I can't say which things are actually used, but this would seem to confirm my above guess, along with the other one - you can use more chemicals in industry than you would in a home.

Product and process of blanching nuts

A product and process of removing the skins from nuts involves wetting the nut kernels with an alkaline solution and then with a peroxygen solution. The two substances react underneath the skin to liberate gas between the nut meat and the skin. The gas bubbles blister the skin, causing it to become loosened. Slight mechanical brushing is used to dislodge the blistered skins from the nut meats.

Method and apparatus for blanching nuts

Two counter rotating rollers are provided having elastomeric exterior coatings into which ribs and grooves are formed for intermeshing to blanch nuts at a pinch point therebetween. Grooves in the lower roller hold nuts as ribs on the upper roller pass across the nuts to break skins on the nuts. The elastomeric exterior coatings have surface hardness values which measure around 30 durometer. The squeeze at the pinch point between the two rollers can be repeatably adjusted for running different sizes of nuts.

Not really helpful for doing it at home. Hard to say which ones are commonly used in industry, of course. You can find a lot more patents along these lines.

Roasting the bones will give you a darker brown stock than using the raw bones. To roast the bones, just stick them in an oven on high heat, around 450 for about 45 minutes, or until they are a nice golden caramelized color. Though you will want to make sure to keep an eye on them the first time, I'd check every 5 minutes after half an hour. Roasting the veggies with the bones will also add a slightly sweeter roasted flavor. It's like the difference of putting slices of raw onions on a burger compared to caramelized onions. You get a slightly sweeter, richer roasted flavor. Though it does turn down some of the other flavor notes, it's up to you which you'd rather have. Without roasting, you'd have a clearer "white" stock.

If you are using the butter as a base to roast the bones, I would set it aside and go with a higher smoke point oil like a peanut or corn oil. The low smoke point of the butter could leave a bitter, slightly burned flavor, especially with the longer roasting times.

I would leave the seasoning for the stock. Most spices will burn at a lower temperature, and salting the bones before you make your stock, could make your stock overly salty. It's easier to add more toward the end, than try to figure out what to do with salty stock.

I hope that helps!