Only in its very last few years, and not as closely as it looks. It had just as much cooperation from the NCC in relation to some matters.
It was more of a consultative aspect, as the BCDR was of course fully independent in all respects.
The SLNCR used the services of some GNR people from time to time, with regard to permanent way and diesel rail uses.
The DNGR, on the other hand, ended up being operated by the GNR, often using their locos and stock.