Major Description
This has to do with HIVE-15575. TezCompiler seems to set mapred.input.dir.recursive to true. This is acceptable for Hive jobs, since this allows Hive to consume its peculiar UNION ALL output, where the output of each relation is stored in a separate sub-directory of the output-dir.
For such output to be readable through HCatalog (via Pig/HCatLoader), mapred.input.dir.recursive should be set from HCatInputFormat as well. Otherwise, one gets zero records for that input.