Here is my experience, or lack of. Here in California to do a survey you need to be licensed. Now you can make all the maps you want, make them as close to accurate but you can not imply in any way that they are survey grade, or survey accurate even if they are unless, you can get a licensed surveyor to put his or her stamp of approval on it.
As for stockpile, and volume reports ours were very accurate but had nothing to do with surveying, so I could highlight a stockpile, or trench, pond (with no water) and get very accurate volume reports, however we never stated a level of accuracy to the client, they were always estimates that proved to be very accurate.
I can tell you that some surveyors see drone mapping as a threat to their long term livelihood, and the way technology is going they should be worried. The flip side to that is owners of survey companies are seeing the potential to reduce survey time but still making the same money, lose on one end, gain on the other.
Some of the surveyors would give me inaccurate data just to screw me up, others were very helpful.