Heres a nice little matrix of current VIOS levels and the corresponding AIX level.

The following link also has some fantastic information relating to NIM installation and backup of a Virtual I/O Server (VIOS).

It has an official answer for one of the questions Im asked the most:

Q: Do I need to use an lpp_source to install the VIO server using NIM?

A: No. All of the device drivers and software packages needed to install the VIO server are in the VIO server mksysb.

I also recommend Rob McNellys latest blog on installing VIO servers.