Does Challenge constitute a combat for purposes like Draven Audacious?

No, Challenge does not constitute a combat for the purposes of Draven, Audacious's ability.

According to the rules and FAQs regarding combat:

• Combat Definition: Combat is a specific game phase that occurs when a battlefield is contested and units controlled by opposing players are present (Rule 437, 438). It involves specific steps, including the Showdown Step where Attacker and Defender designations are assigned (Rule 441, 442).
• Challenge's Nature: As noted in the FAQ, "Challenge doesn't cause a combat showdown itself, it's just a spell doing damage." Because Challenge does not initiate the steps of combat or assign Attacker/Defender designations, it does not trigger abilities that require "winning a combat."
• Draven's Requirement: Draven's ability specifically triggers when he wins a combat. Since Challenge is a spell effect and not a combat, it cannot satisfy the condition for Draven to score a point.

In summary, while Challenge causes units to deal damage to each other, it is a non-combat interaction and does not count as a combat for Draven, Audacious.