Hey Mike. Welcome to the forum.
I would love to be involved in such a project. I have thought about this before that InfoPath could be an additional UI to Dynamics data but have not had an opportunity.
With webservices and the right Architecture I believe you could have a seemless integration. You could both query and submit data to SQL. You would just need to keep it consistent with what Dynamics needed.
You can send me an email and we could discuss further if you want. I could show you some PO forms that are already linked to a SQL database.