I have some people draw with markers in my figure/interior drawing classes. And the instructor is cool with that, I think he actually said it would be good. I must say that, at least with gestural drawing, they just use the markers as "something that makes a mark" and could just as well be using pencils or whatnot. In architectural drawings, the shading elements have come to play better and the different grays play out nicely. But that might be because most of them are more comfortable and trained in that stuff.