I have 2 Dell R710's directly connected with 2 crossover cables in NIC 3 & NIC 4.
If I understand you correctly these two nics are used for vmk3?
With the cross-over connecting this may only work if vmk3 uses the same vmnic on both hosts, which is not necessarily the case.
To find out whether the cross-over setup causes the issue, remove one cross-over cable, so that each ESXi host fails over to the remaining vmnic.
André