AIO subsystems in 6.1 and later are loaded by default and not activated. It is implemented as kernel service instead of using special device aio0 as in previous AIX versions. The kernel module tuning (maxservers, minservers, etc.) is implemented via ioo command.
In order to check the available aio tunables, you must use the following command:
# ioo -L | grep aio

The moment application initiates the AIO I/O requests, the subsystems are automatically started.

gzaix# ioo -a | grep active
                    aio_active = 1
                    posix_aio_active = 0

The parameters aio_active and posix_aix_active can only be changed by AIX, and they are set to 1 only when AIO kernel extensors are used and pinned (e.g. if the application is actively trying to use it).