Hi,
we've both xsigo and UCS in our infra. Both work like charm with respect to the network properties.
In our configurations the Uplinks (vNICs) are from different xsigo directors / UCS IO modules. So its sure that traffic are flowing through different vNICs and it passed through seperate network.
For example
In host1 vNIC0 is from XSIGO director 1 and vNIC1 is from XSIGO director 2.
With respect to ESXi the vNICs are just like a Physical NIC. It will do load balancing and IOC as it does with the Physical NICs.