You can do that:
1) import the route from GPX
2) edit the route with Route Planner if you want (not required)
3) follow the route with Run.GPS
4) upload the recorded training
=> the training will get assigned to the route if it matches exactly enough
One restriction: you cannot use GPX files imported into the GPS-Sport.net portal as Virtual Training Partner because the timestamps are not imported. Therefore, Run.GPS cannot compare the current times to the route's times.
I think was nice to have route competition working with import route from GPX file or allowed to import trainings from GPX file and have competition working.