For each installation of Application Server you must either use all Model 1 licenses or all Model 2 licenses. However, on a single machine you can have multiple installations of Application Server and these can use either Model 1 or Model 2 licenses. Installations with Enterprise Server use Model 2 licenses only.
64-bit on AIX:
If you install the 64-bit version of Application Server on AIX, you receive licenses for the 64-bit version. Any licenses associated with a 32-bit version of Application Server on AIX remain enabled. You cannot use 32-bit licenses with 64-bit Application Server on AIX, nor can you use 64-bit licenses with 32-bit Application Server on AIX.