Does Dream Zanarkand - the one Tidus is from - actually exist? Obviously it is a dream of the fayth and all, but does it maintain a constant progression of time or is Tidus simply "born" into Spira with all these memories?

I feel as though the existence of both Jecht and Tidus gives weight to the idea that the Dream Zanarkand we're exposed to does exist, and Jecht's disappearance from Dream Zanarkand does line up with his arrival in Spira. So there's that. There's also the fact that Auron can seemingly travel between them riding Sin like a badass.