According to the litereature (Novels and Mods) Druids do exist, in small numbers on Krynn. They are periodically monitored by the conclave, as well (See The Soulforge).
"Shifter," as it exists in NWN seems to have nothing to do with being a Druid (undead and construct forms????)
I could see a character like this existing (Until the conclave found out and decided what to do about it).
From a Druid perspective (on krynn) any shape-shifting should be limited to the animal and vegetable world. This makes sense from an RP standpoint, as well as from a LOGIC standpoint. Perhaps in the future, we will re-work the shifter table so that it makes more sense to play.
1) Like people, Druids can come in a few different flavors. True Neutral is the old AD&D rule about them - later additions allowed NG and NE. I can see it. The Druid who has a good heart and want free hippy love between man and tree. Also, the Druid who sees civilized man as an incursion into a holy place. The druid who lures hunters and trappers to their death.
2) I don't really want to start restricting druid versus shifter level, other than to say no exploitative builds. I like to think that this is a mature enough group that everybody understands what we're playing and a druid isn't going to shift into an iron golem in the middle of Solace, during a mage convention! Generally, if it makes sense, plays well, and is fair - RP can open lots of new doors. As to the survival ladder - You know what your playing. Do a crazy race/class combo at your own risk (by "own" I mean the character). A player can ALWAYS roll up another.
3) I've never been a fan of DMs who, flat-out, say "You can't do that!" As it is in the real-world. People can DO anything...as long as they are prepared to answer the consequences. I'm a fan of "Ok, you do that and..."
Some things just can't be allowed. Purple Dragon Knight, for example. Dragonshape. It would unbalance Krynn. Unbalance is another reason that I discourage Sorcerers. It is an overpowered class.
In general, everybody here should be familiar with the ground-rules of what is acceptable on Krynn and what is not. As a story-teller, I am never adverse to new elements, so long as those elements make sense and are in context with the rest of the story-telling tools.