DD,
All recruitment to Cityhopper is via KLM. There is one seniority list and at the outset you can choose long haul SO (Co-Co) or Cityhopper FO.
The bidding process has changed a bit since I left, but essentially KLM pilots can bid for command on the F100/70 and soon EMB190.
Although there is one list, due to the history, it is effectively still three companies (KLM, Cityhopper and the remains of Air UK).
The detail is very confusing, but the principle is fairly straight forward.
KT