Hi,
What is physical host, HP, Dell or any other. If it is from HP, DEll or IBM, then you have to use ESXi 5.1 image from these vendor since they will contain all the VIB, you will not see these option of migrate.
However if you choose migrate still all the third party information will be available ton upgraded ESXi 5.1
Note : If you have virtual machine located on local datastore of ESXi host, first take backup of it before upgrade.
Regards
Mohammed