well I'll see i can take a stab at this one too...(or at least part of it...) I think MH3444 pretty much has it nailed but I'll add a little more info....
Re: "national hideout", never heard that one so not a clue! I think it was probably "National Night Out" too unless you've heard it more recently than early August.
Re: "regional hospital"....my guess, like MH3444's, is that this has something to do with when hospitals go on "TAD" or "Total Ambulance Divert" which means hospitals are overburdened and can't handle the patient load. If Washington County is getting slammed, you'll hear them talk about "Western Zone Management"...if the Portland area hospitals are also closing their ER's due to overcrowding, you'll hear them talking about "central zone management". They'll go onto "zone management" which basically is a way to direct ambulances to different hospitals by having each hospital "take turns" accepting ambulance patients (thus spreading out the patients to different hospitals across the region)
Medical Resource Hospital ("MRH") generally runs "zone management" and you'll hear ambulances calling into MRH to find out "which hospital is up next".
My guess of the around midnight thing is that things generally calm down by then, so you may be hearing MRH (who sometimes also goes by "regional hospital") turning control of ambulances back over to Metrowest.
Our health care system is in a sad state...used to be that area hospitals would only go "on divert" on busy weekend nights.....now it's just about every other night if not more. Will only get worse as people drop health insurance and rely on 9-1-1 to be their primary care doc!
