I farm in central California. I used to grow muscat wine grapes. I have saved a bunch of the stumps and used them for Santa Maria Tri-Tip. It has been nick-named "poor mans hickory" by some around here. Has great flavor. These were more large limb and stump wood with lots of bark. Never tried the prunings. If they work I could get them by the mega-tons! Maybe a new business idea!
The stump wood was pretty intense, but worked well for hot grilling, I would imagine the prunings would be milder and more suitable for slow cooking.