I was reading through WW80064 Scarab's Special Damage power:

THE TRAINING WHEELS ARE OFF: Scarab can count squares for range and line of fire from unheld objects and opposing equipped characters. When Scarab attacks this way, he deals a maximum of 1 damage.

From the text, it seems the power is for attacking only from the statement "When Scarab attacks...". If the intent was for him to use other powers (like his traited outwit) it would say "If Scarab attacks...". So can he use other powers or just attack?

See that period at the end of the sentence it acts just a period normally does so one stops reading that sentence, then a new sentence tells the player something that happens relating to the previous sentence but it doesn't change the overall message that sentence conveys to the player. In this case "Scarab only deals MAX 1 damage when he attacks" is a wholly separate clause that functions outside of the rest of the power but still relates to it