>>55875451No, you can play Sleep without playing Go at all.
If you get the Go Plus+ accessory, you can use it strictly as a sleep tracker.
It unlocks a sleeping cap Pikachu that pitches in a few extra Grepa berries, Apples, and Cacao, it does help.
There's a small daily bonus if you also play Go and sync some play data though.
I must stress small, you can get up to 14 bonus Grepa berries if you spin up to 32 Poké Stops using the Go Plus+'s auto-spinner function in Pokémon Go.
It's such a trivial bonus that it won't make an impact.