Performance-wise, you may have a penalty using a vNICs bond. The physical NIC may have to change mode, while your Guest OS changes vNIC. However, from availability point of view, there may be some small benefit: A vNIC can be blocked somehow, in OS level and then a second vNIC may take over - a very low probability case.
Then, if you physical switch supports it, you may set tag-based VLANs and push it to the GuestOS (linux supports it). This will allow finer-grain control and shaping of your traffic. Alternative routes made by the switch and any router may help in very specific cases or improve HA.
In other cases there may be a benefit, depending on the setup. If your bare-metal has 6 NIC and you directly assign 2 of them to the VM, then, of course, the bonding of VM NIC will be practically a bond of the physical NIC.