If I choose Chthon to be Cap Wolf’s pilot for:

PILOT: WOLF ON TWO WHEELS: When revealing your force, you may choose a single base character on your Sideline that is named Captain America or has the Monster keyword and turn it to any click. Capwolf can use the standard attack and damage powers displayed on that character's dial. // When Capwolf is KO'd, before removing him from the map generate the chosen character from your Sideline on its last non-KO click. This game that character can't be healed or replaced, and isn't scored when KO'd. Protected: Pulse Wave.

Can I also choose Cap Wolf, or another qualifying figure on my team, for Chthon’s trait?

ELDER GOD: DEMON OF THE DARKHOLD: SIDELINE ACTIVE - At the beginning of the game, choose a friendly character with the Mystical keyword. This game that character modifies its combat values +1. When that character is given an action token, if they're not named Chthon, deal them 1 unavoidable damage.

I seem to remember at one time figures could be only on the side line for one specific purpose or another, but I honestly do not know any more.

Thanks for any clarification.