I can definately see a bit of Warhammer 40k's influence here. The abilities sound like something a Templar or Necron would have. (Yes, I must agree...Necrons rule).

Unfortunately, your class does not confrom well to the D&D system. I like where you were going with the class, the flavor is good, but the mechanics need a lot of work.

First, this is definately prestige class material. The goals, motivations, and powers are just too specific to be anything otherwise. Second, many of your abilities (even with a Dex requirement) break the game. To eliminate this problem, may I suggest the following?

Devotee of Keala Mensha Khaine

Requirements
Alignment: Any non-lawful
BAB: +4
Feats: Lightning Reflexes, Quick Draw
Skills:Move Silently 5, Balance 8
Special: Must be initiated into the order by a current devotee
Special: Must endure special training by a current member for a period of at least one month

HD: d6
Skill points: 4 + Int
The Shadow Servants Class Skills (and the key ability for each skill) are Balance (Dex) Climb (Str) Disable Device (Int) Hide (Dex) Jump (Str) Listen (Wis) Move Silently (Dex) Spot (Wis) Survival (Wis) Swim (Str) and Tumble (Dex).

BAB: 3/4 progression
Saves: Reflex good, Fort and Will poor

ABILITIES
Shadow Arts (Su or Sp): Beginning at first level and every other level, a devotee of Keala Mensha Khaine begins to learn special arts that help protect him from harm and make him a more potent assassin. The character may choose one art from the table below. His level plus his Dexterity modifier determine which arts he may choose from. A devotee may only choose a given art once.
TABLE
1: Improved Initiative as bonus feat
2: +2 bonus on Will saves
3: Increase all base speeds by 5 ft.
4: Once per day, the devotee may reroll any initiative roll.
5: Once per day, the devotee may reroll one attack roll. This must be made before the DM annouces the result of the roll.
6: Uncanny Dodge (or Imp. Uncanny Dodge if they already have UD)
7: Critical range of any light weapon wielded doubles (does not stack with similar abilities)
8: Gain Invisibility 1/day as a spell-like ability
9: +1 insight bonus to AC
10: Gain Greater Invisibility 1/day as a spell-like ability

Evasion (Ex): At second level, the devotee of KMK gains evasion. If they already have evasion from another source, they gain Imp. Evasion instead.

Uncanny Dodge (Ex): At 4th level, the devotee of KMK gains uncanny dodge. If they already have uncanny dodge from another source, they gain imp. uncanny dodge instead and levels stack to determine the minimum level to be sneak attacked.

Improved Evasion (Ex): At 6th level, the devotee of KMK gains Improved Evasion.

Blend into Shadows (Ex): At 8th level, a devotee of KMK may use the Hide skill to hide in any shadow illumination, even if it doesn't offer any cover or concealment. A devotee may not hide in his own shadow.

Code of Conduct: A devotee of KMK may not wear medium or heavy armor of any type. However, they may use any magic effect that would grant such a bonus. If they violate this code, they lose all abilities until they attone.

How's that?