Kevin,
HealthKit is meant for a single individual, not 'shared'. HealthKit can be used without an Apple ID. It would be just the same as running on a simulator that isn't signed in. That having been said, while you could technically do it, it is overkill and using HealthKit outside of the intended scope.
I'll speculate that the built-in pedometer will also not have super reliable results given the way each user walks is different. This is what generates samples for HealthKit under the hood. If you're going to pursue this concept, I would instead recommend using the CMPedometer API directly, which allows for up to 7-days of historical data.
Topic:
App & System Services
SubTopic:
Health & Fitness
Tags: