Yes and no. In pinciple you are right, but the rootvg might contain things you deem equally confidential - ssh keys in home directories, wallet files for databases, and similar things.
In AIX you do not need to wipe the OS completely. If you overwrite the first GB (or thereabouts) of the rootvgs hdisk device(s) with hexadecimal zeroes you will destroy the VGDA and upon reboot the...