2 Questions

[cyclops2500 4]

1) Can Holton Salm use his ability endlessly, until either focus/hit/crit comes up?

 

2) Can Vader use his ability to take two evades and then evade twice in one round?

[KineticOperator 2,534]

Both covered in the rules.  Dice cannot be rerolled more than once under any circumstances.  So no, Horton cannot keep rerolling.

A ship may not perform a single action more than once in a turn.  So, regardless of how many actions you have you may only perform each one time per turn.  One evade, one focus, one Target Lock, etc.