1.9.10 is the Ethernet driver it does not support SRP it only support iSER.
1.8.3 is the IB driver which support both iSER and SRP.
That's why you are not seeing SRP in vSphere. I am not familiar with Zadra. But looks like it's ZFS based. If they do support IB you could load 1.8.3 IB driver to your ESXi to see if there is any performance difference.
*I do not work for Mellanox but I do like their product