as rosdep is responsible for installing required dependencies, there doesn't appear to be any point in asking it to continue if it couldn't do that for whatever reason. Failing early while setting up the development environment would be much better.
Technically, the repositories/packages listed in dependencies.repos are not needed by abb_robot_driver_state_machine. The only dependencies really needed are the various messages and services it uses to communicate with the abb_robot_driver node(s).
The latter are already declared as dependencies in the manifest:
The packages in dependencies.repos would be needed if a user is setting up abb_robot_driver itself, but then (s)he would be instructed to download those as part of the setup instructions of that package. An unsuspecting user trying to setup abb_robot_driver_state_machine would run into vcs errors due to it trying to clone repositories which are already present in the workspace.