PAE lets the OS and specifically aware processes address more memory than what a simple pointer can address. If you turn it on then your OS can use more memory. That doesn't let any individual application push the 32-bit limit unless the OS supplies hooks for mapping and unmapping memory into what the program can directly address, and the program is aware of and uses those hooks.

If you had a single process address over 4 GB of RAM on a 32-bit CPU, then the OS has to provide those hooks and the application has to be using it. It would make sense for BerkeleyDB to try this, but I don't know if does. If it doesn't and you want it to, you could pay Sleepycat to develop it for you.