Usually, the rule is "specific trumps general" so a strategem use ought to take precedence over the Inescapable Accuracy rule, since the Pathfinders stratagem does not apply a modifier but instead just changes what do you hit on in the same way that inescapable accuracy does
But in that train of thought, so does the Cullexus Assassin, and GW has ruled that Inescapable Accuracy trumps the assassin's rule.
I disagree. The logic is different.
Culexus doesn't change the number you hit on, just your ballistic skill. RAW without any interpretation or "specific trumps general", reapers hit on 3s vs Culexus because reaper to hit rolls are independent of ballistic skill.
The reason Pathfinders stratagem is different is that it is not a to hit modifier, nor does it change your BS ( both of which are overridden, RAW, by Inescapable Accuracy). Instead, like Inescapable Accuracy, it just says "you now hit on 6s no matter what"-- in other words, unlike Hard To Hit or Culexus rule, it acts directly on conditions for success for to hit roll.
Pathfinders, like Inescapable Accuracy, bypasses it all to impose an absolute condition irrespective of any modifiers. This is a crucial distinction to make: Inescapable Accuracy is in the same category as Pathfinders, mechanically.