I've migrated the vKernel's (one by one, generally with that host in maintenance mode).
After you migrate the first one, you might want to confirm that vkernel can still ping the other vKernel's and that multicast is still working (run the health check being the easy way to do this). The one time it didn't work it was because the VLAN wasn't setup properly on the VDS.
The other option is setup a "B" network for VSAN on a different VLAN/Subnet on the VDS and give each host a 2nd vKernel, confirm they are working then remove 1 by 1 the VSS attached vKernels. (VSAN supports more than one vKernel, just not on the same subnet).