By definition USGS DEM files are supposed to be based on the NAD 27 (E0) datum, however, PCI has noticed some that where based on the NAD 83 datum. The GeoGateway library cannot detect this, and will always report DEM files as being E0 (NAD27).
USGS DEM elevations may be metres, feet, or perhaps even other units. Upon import the DEM channel will be marked with metadata indicating an ELEVATION_UNITS of either FEET, or METRE. Not much PCI software utilizes this metadata directly, but it can be inspected by a user, and a simple model can be used to convert between feet, and metre units.
Areas of missing data in USGS DEM files are set to a background value of zero. The NO_DATA_VALUE metadata is attached to the channel indicating the background value (0). This means that areas of zero elevation are not distinguishable from areas of no data. At some point in the future PCI may change the no data value for this translator to another value, such as -32737, at which point the NO_DATA_VALUE metadata will also be updated.
The PACE task DEMWRIT may be used to write USGS DEM files; however, export support is not currently supported through GeoGateway.