If the cups are oven safe, absolutely.

I think you can. Does it say on the bottom of the cups?

It should be fine. I have used my coffee mugs in the oven plenty of times, from french onion soup to reheating chili. And mine are cheapies from Walmart.

I'm not familiar with that particular dinnerware. Check the manufacturers website for whether it is considered a stoneware product.

In terms of pottery, 'stoneware' is high fire clay and glaze and should be fine at that high a temperature (although not, of course) on a stove top. Earthenware is a lower fired product and I would not recommend that temp.