Roots on elm should always be buried. Elm roots grow extremely fast and are large and fleshy. If not dealt with yearly they will continue to push the tree out of the pot with each passing year. Sometimes like on this tree, the tree can be planted deeper and covered with moss to bring back the feeder roots which issue from the large roots. The large roots can be cut back by as much as two thirds without issue and developed from there. If the roots are exposed for more than a season and begin lignification process, it is very hard to turn them into roots again. This is what most people experience with elm roots, the exposed portion from being root bound in too small a pot and not up potted. Many beginners see these roots and mistake that for something which should be highly prized in bonsai, which it is not.
Flat roots on the soil surface - Good.
Unruly, gnarled roots like a claw - Bad.
Do not confuse roots such as these above with the Neagari style which has roots which are exposed but arranged in a pleasing and lacy fashion. the roots will be singular with lots of space in between and seen to support the tree.
Evans tree could be developed to look that way with little work over a few years by selectively removing some of the roots and allowing the plant to be lifted throughout the year exposing the lengthening roots a little each month. Within a few years the tree will be quite stilted and could become quite beautiful.