I created two GPX files with waypoints; each waypoint was assigned a different symbol, so that they covered every possible symbol in BaseCamp.
After putting the files on an Edge 800 (one at a time because of the maximum number of waypoints the Edge supports), the device transfers the waypoints to the file Locations.fit; after that, the GPX file was deleted (manually).
As expected the Edge doesn't support all symbols; those it doesn't are replaced by a blue flag, but the supported ones are displayed correctly.
The Locations.fit file cannot be imported manually in BaseCamp, but BaseCamp will read it from the device. However, when doing so BaseCamp mixes up all waypoint symbols; no one is correct! This applies to BaseCamp for the Mac too. I did my tests with BaseCamp 4.0.1, but I guess this isn't solved in 4.0.2 (at least it isn't mentioned in the change log).