oggdec prints version string to the data stream when decoding to stdout
here an example:
$ oggdec --output - foo.ogg 2>/dev/null
oggdec from vorbis-tools 1.4.0
RIFF [and some more binary data]
I propose you print out the version string to stderr when in normal operation. I have attached a patch which should solve the problem [untested!] [now tested]