It's start at chapter 3
Went slate join your team and stuff
Never met him. Like the OP I keep getting in a loop with Rohan and have never met Stryker or Hex (or a lot of the characters mentioned in the check list/fake guide)
You need to meet them through Vamp first. Well Skryter, Hex is met through prelude to chapter 3. If you did a chapter 3 skip you'll have him unlocked.