Is Scott rode the icebreaker and the snowmobile a compound subject?

No, "Scott rode the icebreaker and the snowmobile" does not contain a compound subject. In this sentence, "Scott" is the subject, and "rode the icebreaker and the snowmobile" is the predicate, where "the icebreaker and the snowmobile" are part of the compound object, not the subject. A compound subject would involve two or more subjects performing the same action, such as "Scott and his friend rode the icebreaker."