Earth 2, the title, keeps adding references. Some subtle such as Tyler Chemicals in the Background.
Others direct..either by seeing them in person or having another hero mention the person.
As such is the case with Rex Mason..http://dc.wikia.com/wiki/Rex_Mason_(New_Earth) Metamorpho being mentioned in the Earth 2 Annual.
Still think it should have been Rex Tyler http://dc.wikia.com/wiki/Rex_Tyler_(New_Earth the original Hourman. Especially since he created the Miracilo pill that the new Batman uses.
Here is the DC Wiki that give you an update as to who has appeared so far. http://dc.wikia.com/wiki/Earth_2
That is all for now
Go Forth and Do Well