Yes, all users who want to be able to create and work with scratch orgs will need some access to the Dev Hub. Here's Salesforce's own documentation on how to manage Salesforce DX users:
These users will need to auth into the Dev Hub using either shared or dedicated credentials, then they will be able to use that Dev Hub to factory scratch orgs. Once that's done, they'll be able to push and pull metadata between the local filesystem and the scratch orgs, and of course in general the metadata in the local filesystem should be ultimately mastered in a version control system.
As for whether SFDX is useful for non-ISVs, it definitely is. While the migration path to SFDX will be more straightforward for ISVs who have already likely been working in a mode that encourages decoupling of metadata from the org, there is a migration path for Enterprise developers as well. I provided an overview of that migration path in my Pluralsight course, but there's only so much you can cover in 2-3 hours. I described the expected benefits and some potential strategies for extracting and organizing features/products from the "happy soup" so that it can be managed using SFDX tools and processes. For both ISVs and Enterprise developers, there's a non-trivial up-front cost to this switch, but the benefits of it should justify that cost in the end.
I hope that helps. Let me know if you have other questions.
Regards,
Scott Wells