There was a significant change to the Sniper archetype's ability since this question was asked.
The Sniper Archetype's Deadly Range ability:
Deadly Range (Ex): At 2nd level, when the sniper makes an attack against a target who is within his weapon's first range increment and completely unaware of his presence, that attack ignores the 30 foot range limit on ranged sneak attacks, and if it is a sneak attack, he adds his sniper level as a bonus on his sneak attack damage roll. After this first attack, the target is aware of the sniper's presence.
The Slayer Talent's Deadly Range ability:
Deadly Range (Ex): A slayer with this talent increases the range at which he can deal sneak attack damage by 10 feet. A slayer can select this talent more than once; its effects stack. A slayer must be at least 4th level before selecting this talent.
The archetype version of the ability is built-in and deals with a very specific case of performing a sneak attack allowing the character to completely ignore the range limit.
The base class version of the ability is optional and deals with the general case of performing a sneak attack allowing the character to increase the range limit by a moderate amount.
- These two abilities, while similar, are not the same.
- Yes; every time a character takes the Deadly Range slayer talent, his maximum sneak attack range increases by 10 feet.
- The sniper's Deadly Range ability, if it applies, allows the character to completely ignore the range limit on sneak attacks regardless if it is the standard 30 feet or increased by the slayer talent.
- Yes; a sniper can take the Deadly Range slayer's talent. When the sniper's built-in ability applies, he uses it. In all other cases of using sneak attack, he would use the increased range provided by the slayer talent. The sniper's built-in ability would apply for example when he is under the effects of invisibility and/or attacking an opponent from a hidden location for the first time during an encounter. In all other cases, he would use the benefit of the slayer talent instead.