I have checked the MTU, and actually pushed it back down to 1500 across the board. I have tried a vmkping as described and it successfully pings.
I believe I've narrowed it down to a combination of ESXi 5.1 using the qla8152 (latest drivers/firmware) and the Nexus 5020 on the networking side of the CNA. The SAN Side doesn't appear to be having any difficulties.
I'm hoping to get a case open with Cisco in order to figure out how to diagnose any flow control or packet issues on its end, but it kind of feels like at this point that the issue is with the qlogic card.