Since MPIO has load balancing and path failover functionality, it will accept more than 1 path for sure. And yes, you can install it on VIO afaik.
We are not sharing any disks via VIO - only hosting some adapters for our admin LAN with SEA FAILOVER.
Usually we provide for our boxes direct access via MPIO or PowerPath to our SAN storage.

I don't know anything about RDAC, but when you just Google for AIX VIO and MPIO, you find a lot of documentation and also this thread, that might be helpful:
MPIO or RDAC for DS4800 - ITtoolbox Groups

Also 2 Redbooks that might help:
IBM Redbooks | PowerVM Virtualization on IBM System p: Introduction and Configuration Fourth Edition
IBM Redbooks | IBM System Storage N series MPIO Support?Frequently Asked Questions