The correct GNU canonicalization for an ARM based machine running NetBSD is

  arm-unknown-netbsd{version}

I recently installed a change to the official source of config.guess to 
ensure this happens.  In time this will get released into most GNU 
packages.

arm32 is what netbsd calls its port to the ARM processor family; it is not 
what should be returned as the CPU name in the GNU canonical string.

Richard.