All well and good, but by my reading a separate file is not required. From the release guide:
The Incubator Disclaimer
TODO: the incubator requires that users are informed that the by including a standard disclaimer. may be include in README, RELEASE_NOTES DISCLAIMER. It is recommended that it is not included in NOTICES
( see http://incubator.apache.org/guides/releasemanagement.html#notes-disclaimer )
This clearly states that the disclaimer can be in any of several files and that there is no strong preference.
Another view is bound in the branding guidelines
Podling web sites MUST include a clear disclaimer on their website and in all documentation (including releases) stating that they are in incubation. Podlings SHOULD use the following text for all disclaimers (replace the underlined phrases as appropriate):
Apache Podling-Name is an effort undergoing incubation at The Apache Software Foundation (ASF), sponsored by the name of Apache TLP sponsor. Incubation is required of all newly accepted projects until a further review indicates that the infrastructure, communications, and decision making process have stabilized in a manner consistent with other successful ASF projects. While incubation status is not necessarily a reflection of the completeness or stability of the code, it does indicate that the project has yet to be fully endorsed by the ASF.
Podlings wishing to use a different disclaimer message MUST have the disclaimer approved by the Incubator PMC prior to use.
For releases, the text SHOULD be included in a separate DISCLAIMER file stored alongside the NOTICE and LICENSE files.
(see http://incubator.apache.org/guides/branding.html )
The text here clearly and explicitly uses "SHOULD" rather than "MUST". Citing standard usage from RFC-2119 (see http://tools.ietf.org/html/rfc2119 ), this usage defines recommended practice, not required practice.
I don't think that this is a release stopper by any means.