I have a 32-bit application which also has a device driver. I am using the DIFXAPP support in WiX to install the driver. Is it OK on 64-bit windows to install the application and 64-bit driver files to a subdirectory of Program Files (x86) then have DIFX install the driver to the driver store from there? I believe that it's not allowed to run 64-bit code from the 32-bit Program Files directory but in this case I'm not running it, just asking DIFXAPP to copy it. The actual function used is DriverPackageInstall().
There is a convention to install programs 32-bit programs into the x86 tree, but it is not forbidden. It is legal to copy the DIFXAPP executable and accompanying files into a sub-directory in Program Files (x86) and start it from there.