Just tested it........
Within Sound Forge itself, the Bit Depth plug has no problem converting 32-bit files to other bit depths.
Within the Batch Processor - apparently, the same plug doesn't like to handle 32-bit files - the result was a zero-amplitude file like you described.
If I used a 24-bit version of my sample clip, however, it worked correctly from within the BP....
Looks like a bug in that Batch Processor.......!
I guess the workaround is to manually convert your files within Sound Forge itself.......
Personally - I never work with 32-bit files (24-bit is plenty!), so I've never noticed the bug... I wonder if it's been fixed in Sound Forge 7?