I am working on setting up 40G infiniband networking for TrueNAS storage server
My reason for this setup is to help reduce latency when reading/writing to the TrueNAS storage server
Computer nodes will be connected via 10G SFP+ ports to mikrotik switch
So lets say i have a switch like mikrotik CRS326-24S+2Q+RM https://mikrotik.com/product/crs326_24s_2q_rm with 2 x 40G QSFP+ ports
So what am thinking is get Dell R730xd and get 40GB infiniband card, connect that to the 40 QSFP+ port on the switch and then have TrueNAS be consumed servers connected to the same switch via the 10G SFP+ ports. Is this setup good to have reduced latency to consume storage on TrueNAS core setup via infiniband?

Is that an accurate assumption/expectation setup? or what am i missing?

Ethetnet and infiniband are different L2 technologies and you can't mix them. Mikrotik AFAIK doesn't support infiniband at all.
Some cards support both infiniband and ethernet, but you'll have to configure it to use ethernet.