This post by MrCow breaks down the different attack speed types. Same bonus types don't stack, different ones do.
http://forums.ddo.com/showpost.php?p...85&postcount=3
For specific answers:
1.) Does haste override all item alacrity?
Only if it's an enhancement bonus. Most items are though.
2.) Does the Ranger Capstone Enhancement stack w/ items like the Mod 9 Arcane Archer/Deepwood Sniper Set?
No, they are competence bonuses and don't stack. It will stack with any other bonus type though.
3.) How is the Deepwood Sniper Set bonus considered a competence bonus?
Because that's the bonus type assigned to it.