Not sure I understand what you mean by "... it will inserts its own dummy rdma driver"
Mellanox OFED derives from Open fabric and the rdma modules within Mellanox OFEd package are aligned with the standard RDMA
I also assume you have installed mlnx_ofed v3.4.2 using the pre-required --add-kernel-support flag
However if you use NVMEoF with mlnx_ofed you need to ensure that your Linux kernel version is 4.8.x , other wise NVMEoF is not supported
Have you ensured that RDMA layer is configured properly and that it is running?
this is mandatory to implement and test before running nvme-cli. (use tests such as ib_send_bw,ib_write_bw)
Make sure the Mellanox adapter is on the top of the latest fw
In case above is implemented and problem persist, suggesting to approach mellanox support and open a support ticket for further assistance