I think dual VIOS is out of scope in entry-level servers.
One of my customers has a very reasonable paradigm:
Entry Level servers (550Q - NON-Production Environments) :
VIOS / NO HACMP
High End Servers (they skip 560Q - Production):
570 -> Hardwares Level Partitioning / Some servers use VIOS (2 in cluster)
590 / 595 -> Hardware Leve Partitioning + HACMP
Redundant VIOS is useful in redundant hardware. Maybe you can setup a VIOS with enough availability :
2 NICs , defining 2 Virtual NICs to every LPAR
Mirror your VIOS installation
2 FC Cards - If you are paranoid enough, you could use LUNs from both adapters and make a mirror in your
AIX/Linux between them.
2 RAID Adapters (IOA Level Mirror)
Remember to user enough processor and memory for your VIOS.
Hector Servadac