I've kept emersed swords in the past and about the only critical factor I've found with them is space. In general they do need a relatively humid environment, though not as much as Crypts or stemplants. In a regularly humid environment like the US Southeast a moist soil and daily watering will do the trick. As long as there's enough moisture in the soil for the plant to draw up to compensate for evaporation swords will do just fine. Tom's found Echinordorus in what looked to be a pretty arid part of California growing with their feet in a stream.
I too have grown Echinodorus emersed. In my experience, they do require a certain amount of humidity while adapting to emersed growth. Their emersed leaves have a thicker cuticle (that waxy covering) that helps retain moisture in the leaf.
Once the plant has adapted to emersed growth well, you should not have a problem keeping them in an aquarium with a partial lid on it.