I've always been under the impression that you could never VMotion a VM that has an active connection to an internal switch (with no link to any pNIC), but you actuall can. In order to do it, you have to add some particular lines in the vpxd.cfg file on the VitualCenter Server itself.
C:\Documents and Settings\All Users\Application Data\VMware\VMware VirtualCenter\vpxd.cfg
and add the following lines to the bottom of the cfg file.
< test >
< compatiblenetworks >
< vmonvirtualintranet >false< /vmonvirtualintranet >
< /test >
< /migrate >
You have to create this section at the end of the vpxd.cfg file but still in the section.
Note: This is not supported by VMware but is very handy and you also need to remove the spaces in the < >!