Can a Witch tell whether their Misfortune Hex succeeded or not? If so, how? Also, what about some of their other hexes like Evil Eye where even failure should look the same as success (if it was visible at all)?
Spellcasters intuitively know when the target of their spells fail or succed saving throws.
Succeeding on a Saving Throw: A creature that successfully saves against a spell that has no obvious physical effects feels a hostile force or a tingle, but cannot deduce the exact nature of the attack. Likewise, if a creature's saving throw succeeds against a targeted spell, you sense that the spell has failed. You do not sense when creatures succeed on saves against effect and area spells.
Although this section talks about spells, it's reasonable to extend it to apply to spell-like and supernatural abilities, including hexes.