I don't know how to set RR as the default, but it is possible to script the setting of all storage of a particular type to using RR - I'll see if I can dig up a rough sample for you to start with, but for now here is an outline from memory:
list= use "esxcli nmp device list" to get a list of all devices, use awk to limit it to certain devices, eg exclude local disk
for item in list, do
esxcli nmp device setpolicy -- device $item RR
done
But, yes, I suspect there is a way of setting RR as the default for all new storage devices.
