Every airline in Europe operates that way. They all have multiple certificates, with multiple contracts, through multiple sourcing companies.

BTW, the pilot contracts have nothing to do with where the certificate or holding company is located, it has to do with where the crew is actually based. SAS crews in Copenhagen operate under a different contract and different union than SAS crews in Stockholm, and both are different than the contract and union the SAS crews based in Oslo operate under. NAI 737 crews who were based in Copenhagen operated under the same union and contract as NAS 737 crews based in Copenhagen. NAS crews based in Copenhagen operate under different contracts and unions than the NAS crews based in Oslo. British Airways A320 pilots based in Gatwick operate under a different contract than British Airways A320 pilots based in Heathrow even though they operate under the same union. A senior BA 747 FO based in Heathrow would lose his or her job before a more junior A320 FO based in Gatwick simply because of where the fleet reductions were coming from. When Aer Lingus has crews based in Belfast, they operated under a different contract and union than the crews based in Dublin.

Not defending the system at all. But Europe is a VERY different animal than the US. Most US pilots would not recognize how things work over here with regards to union contracts, seniority, bidding, etc.