The plmxml file will ONLY contain objects where the routepath is routed to a multiport, fixture port or a fitting port. For objects like clips, grommets, backshells, you will need to have a single fixture port to which you route the routepath. Connectors and splices should have a multiport. NX does not have an explicit backshell type, and so it exports it out as a Fixing.
In VeSys, by default, we treat a Fixing as a Clip. But if you had defined the backshell in VComponents as group Other that is how the bridge will treat it and place it in the Other Component folder.
Recall, VeSys does not support an explicit backshell type like Capital does, so having created it as group Other, add it as an additional part in the Housing tab of the connector part number. This may be a better option because the styling of the connector and its additional components should be easier to define.