Have you seen sleep apnea cause fibromyalgia-like unpredictable/"roaming" pain? if so, any idea why?

Yes sometimes: Sleep apnea causes disruptions of normal sleep architecture ( √ wikipedia). This can cause low level (i.e. You're still functional) neurologic changes that are different from person to person. Changes in mood, attention span, critical thinking, etc. Can occur. Chronic pain or inappropriate pain can be one of these low-level malfunctions.

They are related: Fm, TMJ & osa are related. Tmj (bite) problems impairs physiology and acirvates the hypothalamic-adrenal-pituitary (hpa) axis, a main regulatory system. This common pathway can lead to many physiologic disturbances, including problems with sleep and fibromyalgia.

O2 Deprivation : Many issues come to the front if one has sleep apnea. Oxygen deprivation on a chronic scale means that the body is functioning on a third or more less o2 than it requires for extended periods of the night. Muscles need o2 and waste metabolites being removed or they build up Lactic Acid and get more trigger points. Get a sleep study, treat the sleep apnea adequately. Oral devices can help many.