Some are RNG, some aren't.

For instance, the one behind the house with the ogres in the Blighted Village appears to be the same every time. Along with the one along the trail--by the river's edge--along the trail from the village to the swamp. If those are RNG, then they're *very* likely to give the same items.

Also, the one under the bridge by the toll keeper... I think. I haven't had a chance to test that one enough.