Can Captain America, Champion Licese redirect an attack into a hidden character? I was under the impression that the target had to be legal.

Captain America, Champion License

Leader: Remove an adjacent defender from this attack -> Target non-stunned, non-defending character you control becomes a defender. Use only once per turn.

Whenever Captain America becomes stunned, adjacent characters have invulnerability this turn.

His text only specifies that the character you choose be a non-stunned, non-defending character. You can redirect into the hidden area as long as the character you choose fits these modes.

Thanks for clearing that up!