Sadly this appears to have been a case of PEBKAC or PICNIC, looks like I had a typo in the names of the index with the metadata in it and an older one w/o the metadata. Sorry for the annoyance. Using reader.getCommitUserData() is working just fine, I'm able to retrieve the metadata I stored in the index.
Thanks for all the help, -eric p.s. the luke source uses getCommitUserData() as well, to round out the info for those who may come searching later.