A surface is a union of facets. A body is defined by giving its bounding facets. There are no limitations on how many edges may share a vertex nor on how many facets may share an edge. Thus arbitrary topologies are possible, including the triple junctions of surfaces characteristic of soap films. Edges and facets are oriented for bookkeeping purposes, but there are no restrictions on the orientation of neighboring facets.
Unoriented surfaces are thus possible.
A surface is deemed to have a total energy, arising from surface tension, gravitational energy, and possibly other sources. It is this energy which the Evolver minimizes. No particular units of measurement are used. The program only deals with numerical values. If you wish to relate the program values to the real world, then all values should be within one consistent system, such as cgs or mks.