Yes, you can use an Enterprise Apple Developer license to distribute your iOS apps private (i.e., without the App Store).
You can also create Web Apps and host them on your internal network (though offline storage is limited).
However, there is a solution that—in most cases—is better than both of these for distributing offline content to salespeople, and it's known as Sales Enablement.
Sales Enablement is a process or a platform that makes it easier to sell a product, especially a complex product.
Many sales enablement platforms come with a Content Management System (CMS), shared directories, and mobile apps.
The mobile apps let salespeople access up-to-date presentations on their mobile device (offline) so that they can present to potential customers (even in an elevator).
Thus, Sales Enablement is a bridge between content creators (i.e., marketing & design) and the people inside their business who need to use that content (i.e., salespeople).
Marketing & Design > cloud repository > salesperson’s mobile device > in-person pitch
There are several platforms that support HTML (as created by InDesign & in5) content for sales presentations.
- Vablet (see the webinar recording below)
- Mobile Locker
These tools make it easy for you to "push" app-like content to salespeople (and have it be available offline), but you don't have to go through the hassle of actually making an app. You just upload your HTML content to the platform and choose who will have access.