I have an HP z820, dual processor, the latest BIOS J63 v03.65. It’s running RHEL 6.5, has Cuda 5.5 and Nvidia driver 331.49 installed. It has a K600 GPU for display in slot 6 and a K20c GPU for compute in slot 2. Both GPUs are recognized by lspci and the nvidiainit.sh script creates /dev/nvidia0 and /dev/nvidia1 devices for them. But when I run deviceQuery, only the K600 is recognized. The K20c is not recognized.
If I swap out the K20c for a T2075, then the K600 and T2075 are both recognized.
If I take the K20c to my z420, then that computer recognizes its Quadro 600 and the K20c.