Yes and no. Short answer is you need to apply a bonding agent to the durock so the plaster will stick. Blueboard is chemically treated to accept plaster, durock is not so it will just fall off without a bonding agent.
Yes, you can, but it seems a waste of money as durock is much better material.
No, it must be screwed. - But there are many varieties of excellent concrete board now. -
If one side of the drywall is green, it is actually green board. Green board is made with concrete, and is intended for high humidity areas. It will not mold or mildew the same way normal drywall will in moist conditions.
No, it is better caulked with a water resistant caulk. ( Also it should be at least water resistant drywall or concrete/fibre board.)
You COULD, but there's no real need to.
If you expect your shower to last, then remove that drywall and re-finish it with concrete/fibre board. It's so much better than drywall you wouldn't believe it. Nobody professional does drywall around a shower anymore.
If you want to do a really good, lasting job, use concrete/fibre board (Green board) instead of drywall. It comes in 30x60 sheets, about the same cost as drywall, easy to work with , totally water resistant and excellent for tiling. About 4-5 kinds available, Rona and HD each have 2-3 types.
White is the colour of standard drywall board
Cement board, at most contractor supply places it will be called DUROCK cement board or Permabase cement board. = =
Replace the drywall with tile backer.
It will, but PL Premium is better
That's definitely a good idea. If there is a sink and tub in there,I would even use a concrete or fibre board to back them also.
Mildew proof drywall is best out of drywall choices, -but much better still is concrete/fibre board. These are now plentiful and low cost, totally impervious to water and great for tile. Last time I was in Home Depot they had 3 kinds. I always these around bathtubs or shower areas.