So you have alot of virtual machines on your Hyper-V host and you want to load balance the traffic across multiple NICs. Will this help or hurt?
It actually depends on your connectivity from the Hyper-V host to the backbone. If the host is using gigabit NICs and the backbone is gigabit, then you are not gaining any performance improvement. If you use gigabit switches, does the traffic from the Hyper-V host stay within the switch? If so what the backplane performance of the switch? If it is multiple gigabit but the uplink to the backplane is still a single gigabit link, then you will gain advantage between devices that are connected to the swtich, but not across the backbone.
TIP: Map your network speed from the Hyper-V host to the backbone. If there is a single link in the chain that is not faster than the NIC you are installing in the Hyper-V host, then you will not see much if any performance inprovement.