The anser is that SqueakDBX and OpenDBX "should" work on 64 bits. The problem is that it requieres a lot of time because you need to compile in 64 bits by yourself all of these things: Squeak or Pharo VM, FFI plugin, OpenDBX and finally the database client library.

In addition, there are some known problems when using FFI in 64 bits. See http://bugs.squeak.org/view.php?id=7237

So...the shorter and easier solution is to use everything with 32 bits. The VM can be download from the website or compiled by yourself. Maybe, using CFLAGS="-m32" CXXFLAGS="-m32" or something similar. Then you can download a database client library already compiled for 32 bits, or again, compile it.

You can read the following post for more help: SqueakDBX with MySQL in Snow Leopard 64 bits