Unfortunately no, you can't turn models into dem information, you can export terrains as image files (in the terrain editor) but you can't turn those into DEM files by themselves. As for the mt. st. helens problem, we actually already have the dem files, we're trying to get them into Vue with as little alignment work and seam issues as possible, so far we seem to be stuck importing multiple 2048 x 2048 terrains directly from the dem files until E-on improves their dem support to increase the allowable terrain import resolution.