Salam Ahmad,
Yes you can, using vcenter convertor you can do v2v migration while the vm is power on, converter is handling the last changes while you do the migration.
Basem
Another community thread which says you can use cold conversion and powered on vm conversion..
you might have to take care of stopping certain services which cause high IO.. and wait for synchronization.
convert HV VM (P2V) as physical or from Hyper-V server (V2V)