Originally Posted by Muckus

Yes, this is true. I have flown on many Z fare tickets on UA (even before I was *G or joined the RCC) and always had lounge access. Any paid or upgraded international C or F ticket gets you lounge access, with the exception of the arrivals lounge which must be on a paid C or F ticket (I have used UA arrivals lounges on Z fare tickets, by the way, although I think you maybe are supposed to be on a full-fare C ticket or higher).