Based on the Daisy docs shown here:
http://kb.daisy.org/publishing/docs/...ityHazard.html
that should be absolutely correct.
I am just not sure why it is even needed if there is no audio or video resources. Have you added the metadata that tells the user that this is a text only epub:
ie:
schema:accessMode
schema:accessModeSufficient
set to be "textual".
See:
http://kb.daisy.org/publishing/docs/...ccessMode.html
http://kb.daisy.org/publishing/docs/...ufficient.html