Right now the plan is to do Rebellion beta access direct download from Stardock only.
We will continue to issue updates to the existing titles via the GameStop app and via direct download from Stardock, as needed.
So, pre-order will be through StarDock controlled services only (no Steam) as will the beta access be through StarDock controlled services only (no Steam). All updates to the beta version will also be from a StarDock only controlled service (no Steam). At least as far as I can tell from this post.