I don't believe it is changable on the ESXi host, however I suspect your problem maybe upstream if you are having problems contacting hosts after they have been vMotioned.
As a vMotion occurs the host will send a TCP notification that the MAC is no longer on the original host and the switch will start polling a "Who is?" looking for a MAC response in order to update the CAM table.
I think from the description of your problem that your switch is not accepting the signal and CAM is not being updated, have had this problem myself and it required a software update on the switch stack.
Hope this helps.