This is something I've been wondering, since it directly impacts the concept of a character I'm planning. Could a druid be part of the Shadow Tribe, and thus worshiping the Shadow Death, while still being able to cast spells and use druidic abilities?

I presume the Illustrious Serpent, being a mortal creature, cannot grant spells. However, would he allow his subjects to have a patron deity other than himself (Which would really be NO patron deity for reasons mentioned)?

All druids have to worship a nature deity. The shadow dragon is not such a being.

As to whether the shadow dragon would let a servant worship a being other than he, I'd say thats a FOIG answer (if you're applying for a pre-existing member of the Shadow Tribe, run the idea past a DM first).

Hope that helps!

Okay then, one more question: Do shadow dragons breathe fire?

No.