I regret that I have not moved the boot volume group before and don't have a server I can try it on available. I would have to defer to those wiser than I on the procedure to follow. Have you...
When I have migrated LVM managed volumes in the past, we would:-
Present the new LUNs
Grow the volume groups be adding the new LUNs
Use pvmigrate, pvmove or migratepv (as appropriate to the OS...