Been a while but found some of our old docs on this which seems still valid. You can't access a collection of all user profiles, but you can ask a user profile for specific account identifier... so as long as you have the account names, you can access user profiles.
If you'd do this through Graph, you won't get access to potential additional SP user profile properties, which could be there... we do not really recommend them as such, but they can be useful in many scenarios until the proper integration is there with AAD and SP User Profiles.
