I decided to check out the grape cuttings we stuck into sand after we pruned in spring.  I think we have 19 cuttings and all but one have roots:

It's truly incredible how well everything roots in the greenhouse.  We used the sand from the wash at the bottom of our lot and not only did the grapes grow great roots, but it was easy to get the cuttings out of the pot.
I transplanted into gallon water bottles and plastic juice bottles since we're running low on pots.  In the plastic bottles we can see the roots and when they're ready to transplant.   I added some of our regular soil mix to the sand and we'll definitely leave the transplants inside for a few weeks.
We also have a big tub with cuttings outside in the shade under the camper, but they didn't grow nearly as much and probably few or none have roots.