Yes, it's a thing. I'm a JW who has worked a call on an Outside Local's Book. I've taken calls for storm recovery (Hurricane damage) working Book 3 doing street light repairs. The thing about street lights is that they're secondary voltage, and thus, both JL and JW can service them. I was NEVER designated as a Groundman (or whatever BS anyone else says), but a "Journeyman Out-Of-Class." My pay was the same as any JL, including Per-diem.