Two Institute of Medicine standards and an AHRQ guide say that one should include librarians:


1. IOM recommends standards for clinical guidelines, reviews

The Institute of Medicine today recommended eight
[ http://iom.edu/Reports/2011/Clinical-Practice-Guidelines-We-Can-Trust.aspx]
standards for developing clinical practice guidelines, and 21
[ http://www.iom.edu/Reports/2011/Finding-What-Works-in-Health-Care-Standards-for-Systematic-Reviews.aspx ]
standards for conducting systematic reviews
of the comparative effectiveness of medical or surgical interventions.
Congress requested the recommendations in the Medicare Improvements for
Patients and Providers Act of 2008. Clinical practice guidelines are
informed by a systematic review of evidence and an assessment of the
benefits and harms of alternative care options. "Because of the large number
of clinical practice guidelines available, practitioners and other guideline
users find it challenging to determine which guidelines are of high
quality," IOM said. "If guideline users had a mechanism to immediately
identify high quality, trustworthy clinical practice guidelines, their
health-related decision making would be improved -potentially improving both
health care quality and health outcomes." (from AHA News).


2.  the new AHRQ guide for effectiveness and comparative
effectiveness reviews also specifically mentions including a librarian.

Relevo R, Balshem H. Finding Evidence for Comparing Medical
Interventions. 2011 Jan 5. Methods Guide for Effectiveness and
Comparative Effectiveness Reviews [Internet]. Rockville (MD): Agency for
Healthcare Research and Quality (US); 2008-. Available from
http://www.ncbi.nlm.nih.gov/books/NBK53479/ 
PubMed PMID: 21433408.