Physicians use ANA tests to screen for autoimmune activity and diseases such as lupus. The problem is that ANA tests can show up positive in inflammatory as well as autoimmune conditions and often show up positive in FM patients. In fact they're positive in about 15% of healthy people as well. So long as more specific tests are negative, just speaking as a layman, I would think your fibromyalgia/chronic fatigue syndrome (plus) diagnosis would hold.
Here's a good article on the ins and outs of ANA testing http://www.prohealth.com/library/showarticle.cfm?id=3601&t=CFIDS_FM