Sure, doing multiple #ifdef's makes sense.  Do you need me to provide an updated patch, or is this something easier for someone who has commit access to the source code repository to just go ahead and do.

I would think this Module would fail to compile if OSS isn't present, no?  So I guess I do not understand your comment about this possibly causing any sort of crash on import at runtime.

The Modules/ossaudiodev.c file should not compile if 
/usr/include/sys/soundcard.h isn't available with OSS definitions.  It wouldn't be on Solaris 10 or earlier.  Is it okay to try and compile this plugin and let it fail if it does?  Or does the configure script need to check this first and only try building it on Solaris 11 or later?