Can ekranoplans (GEV) be more efficient than traditional airliners? Ekranoplans or Ground Effect Vehicles (GEV) fly low enough to the ground that their wings stay in the ground effect. This increases lift and efficiency. 

But GEV fly in the lower atmosphere (literally ground level) which greatly increases drag compared to flying in the stratosphere. 

Is it possible that a GEV designed using contemporary composite materials and high bypass engines could be more efficient per cargo weight-mile (or passenger mile) than a tradition airliner? Or are GEV inherently less efficient due to the altitude they fly at?

This question is specific to fuel efficiency over distance. Feasibility, safety, navigation, time, and cost of airframe are not part of the equation.
As some of the comments above (which are really on the money) suggest it's a complicated question to answer because it is a case of "horses for courses" and that is even if we focus purely on straight-forward fuel efficiency. But given the programs that have been attempted (or are still ongoing) and also various studies it seems that ekranoplans seem to work best in two very distinct roles. Either as small, short range puddle-jumpers or as very large trans-oceanic monsters. For the later see also this which may well come to pass. 

I guess at some level such utterly different roles is a problem for ekranoplan development. But, yes, in principle, there would certainly appear to be certain, very different niches, for which the ekranoplan is extremely competitive in terms of fuel consumption. Having said that the second niche is arguably also competing against conventional surface sea-freight which of course complicates matters but offers interesting possiblities. Aircraft like the Boeing Pelican (which didn't get past concept stage) was designed not for standard air-cargo pallets but for ISO containers. Now that capability is a real game changer as long as the cost per kg/km fuel economy is as good or better than a conventional air-freighter which I suspect is very doable. At least in principle.