So you only upgrading one host in the cluster to 5.1? or only 1 is having a fresh install?
The DVS settings are set at the vCenter level and you just add hosts into it, so the DVS setup is not going to change. If you want to preserve which pnics are connected to which uplink and ip address for the vmkernal adapters then you will need a host profile like solution but i dont think making a profile of a 4 host will be able to be applied to a 5 host.
Think it would be best just to document what is what and it only takes a couple minutes to add back a few ip addresses etc.