As I read the RAW, they are both unlabeled damage enhancements. Wouldn't that make them the same and not able to stack?
Arcane Strike (Combat)
You draw upon your arcane power to enhance your weapons with magical energy.
Prerequisite: Ability to cast arcane spells.
Benefit: As a swift action, you can imbue your weapons with a fraction of your power. For 1 round, your weapons deal +1 damage and are treated as magic for the purpose of overcoming damage reduction. For every five caster levels you possess, this bonus increases by +1, to a maximum of +5 at 20th level.
Deadly Aim (Combat)
You can make exceptionally deadly ranged attacks by pinpointing a foe's weak spot, at the expense of making the attack less likely to succeed.
Prerequisites: Dex 13, base attack bonus +1.
Benefit: You can choose to take a –1 penalty on all ranged attack rolls to gain a +2 bonus on all ranged damage rolls. When your base attack bonus reaches +4, and every +4 thereafter, the penalty increases by –1 and the bonus to damage increases by +2. You must choose to use this feat before making an attack roll and its effects last until your next turn. The bonus damage does not apply to touch attacks or effects that do not deal hit point damage.