If I understand clearly what you're asking for Vellum, you can both hand draw and scan your elements (basically what I've done on Sevindel's harbour) or digitally draw and turn the elemnts to brushes (what I've done on the Kingdom of Ereborn's mountains for example - well the lines were hand-drwan then scanned, then I added paint style shading digitally). To turn some elements to brushes on PS, be sure that you work in black and white or grey tones and make Image/adjustments/Threshold to fit the good contrast, then when you're satisfied, select your element, go to Edit/Define pre-defined form and voilà! You have your awesome brush. Well at least it's the fastest and the easier way.