Yes, but not for everything.
Using the MagicMobile express card on the watch works great for park admissions, lightning lane checkins, PhotoPass scans, buying things and charging it to your on-property room, ride lockers for Tron/Flight of Passage, and checkins for early magic hours with the cast members that check on the tablets.
It won’t work as a room key for on-property resort rooms, do any of the interactive firework/parade light syncing (MagicBand+ light-up stuff), or interactive wireless ride PhotoPass/queue interactions.