A brand-new or factory reset Pokewalker will need to be synced with a HGSS save file before it allows any functionality, including the step counter. Once it has connected to the game once, the step counter will always be available as long as it has power. The dowsing minigame will also be accessible, even without a Pokémon in the Pokewalker. Since Pokewalkers at this point are all pre-owned, there's a chance it might still be paired with the previous owner's save file, in which case you could use the step counter without owning HGSS.
So basically yes, unless the previous owner activated it.
Source: experience