Hello,
Yes, you need at least the ethernet driver and low level driver - mlx4_en and mlx4_core which is why it looks to me that there's something wrong in your installation. it is not related to VMA but to the entire driver functionality.
is it possible you already have existing packages from the RHEL inbox driver loaded and then you installed the Mellanox OFED driver ? can you uninstall the driver again, make sure nothing is loaded and install ?
or alternatively and even a better option, after uninstalling the driver, use the mlnx_add_kernel_support script in the ISO to compile the driver on your kernel, enforcing building the driver packages on your existing packages, once the new ISO is created just load it as you would and do mlnxofedinstall --with-vma again.
Thanks,