If you are looking to migrate from Nexus 1000V to VDS:
Create your destination dVS in advance. Assuming you have multiple physical uplinks per host, you'll want to remove at least one from each host and assign to the new dVS. After that you can start moving guests to the correct port-groups on the new dVS. Once there are no longer any guestVMs utilizing the N1k port-groups, then you can remove the remaining physical uplinks and add them to the dVS.
Using the native VMware 'migrate Virtual machine networking' applet, you can move all guestvms per port-group at a time. You should only have a brief traffic interruption while arp processes reestablish connectivity of the guestVM NIC on new dvs port and associated uplink.
If, for some reason you have only one uplink per host,,, then this probably require some down time.
Found a Cisco reference forum: vSphere - Migrate from Nexus 1000v to v... - Cisco Community