To see whether or not you're able to cast a morph card as a morph (and this applies to any morph card, not just
Zoetic Cavern), first imagine if that card was already face-down–as a 2/2 with no name, color, creature types, etc.–in the zone it's already in. Would you be permitted to cast that card? If so, then you can put it onto the stack face-down and continue casting it as a morph. If not, then you can't. It's really that simple.
So no,
Crucible of Worlds,
Ramunap Excavator, and
Courser of Kruphix do not allow you to cast
Zoetic Cavern as a morph from your graveyard or library, because these cards only allow you to play lands, and the 2/2 morph creature is not a land.
Casting a morph creature doesn't count towards your one land per turn limit, because it's not playing a land–it doesn't matter what's on the front face of the card.