You will want to look at the script William Lam wrote, my organisation has tested this for a huge migration from legacy to HCI environment.
Automating Cross vCenter vMotion (xVC-vMotion) between the same & different SSO Domain
i am new to Power CLI do know how to use it... need help
one more query regarding RDM vms.
how to migrate RDM VMs to Hyper converged system.
Afaik you should be able to do this with the Move-VM cmdlet since PowerCLI 6.5R1 (see the Release Notes).
Kyle did an excellent post on xVC vMotion in Spotlight on the Move-VM Cmdlet including PowerCLI 6.5 EnhancementsBlog: http://lucd.info | Twitter: @LucD22 | PowerCLI Reference co-author: http://tinyurl.com/hkn4glz