Everything that affects bows affects crossbows as well (damage multiplier, etc.), even "Deadly Aim". Those perks that aren't immediately obvious work like this:

 - "Hunter's Discipline" - more bolts (from mobs who drop bolts in the first place)
 - "Ranger" - move faster while aiming and reloading
 - "Quick Draw" - faster reload

The mechanics of the weapons can be confusing.

 - Bow: Ready → draw → aim → shoot → ready.
 - Crossbow: Ready → aim → shoot → reload → ready.

Quick draw yields faster draw for bows and faster reload for crossbows. Ranger lets you move faster while aiming with your bow or crossbow. The thing with a crossbow is that you aim an already loaded weapon, and with the bow, the draw action is part of the aiming. In the end, there's no real difference.