IOS – Pushing offline viewable content to iPads for Enterprise

Each client will need to have an enterprise account. If they want to, they can share their distribution key with you, and you can build an app for distribution within their organization. If the number of clients isn't large, this shouldn't be a big deal -- you can just set up a different target for each client, and then use an aggregate target to build them all at the same time.

Over the air distribution is definitely possible. One way is by making the app available for download on a restricted access web server; another is to install it directly on any managed devices using mobile device management.

I believe most of your questions are answered in the enterprise program agreement. Give that a careful reading if you haven't already. Questions about how to interpret a legal agreement are probably off topic for this forum, but I think you'll find the agreement to be fairly easy to understand as legal documents go.

Update: Another option that's been available for a while now (though possibly not when I wrote the answer above) is custom B2B distribution. You can offer your apps for sale through Apple's Volume Purchase Program directly to your clients. That is, your clients would purchase through the Volume Purchase Program (essentially the App Store, but multiple licenses) and then distribute your app via Mobile Device Management or redemption codes. The down side of this plan is that Apple would take the usual App Store cut of the selling price.

Since no one could answered this I tested it out and found a solution using OSX Server and no need for DEP.

I turned on my macbook pro and purchased OSX server in the app store. Once installed you should be able to go to your local ip or whatever the host name is that your server assigns you, something like markuss-macbook-pro.local. Depending on your settings and network setup you may need to add this in DHCP or DNS, personally I have an Airport Express and the .local domain worked for other Apple devices out of the box.

I was unable to find this online but OSX server comes with Tutorials under Help->Tutorials which shows you how to add devices and push remotely. See the image to see what it looks like

Basically you need to enable the profile manager in the top right corner of the profile manager page and configure Device Management. Once this is done you can go to your url, something like myserver.local/mydevices/ on your iPad or iPhone (make sure you use Safari). If you don't have a valid ssl you will need to accept the insecure connection.

After this was done I was able to manage my device, push apps, change settings and wipe it as long as it was connected to my local network. It seems that you will need a valid domain and SSL certificate that points to your OSX server in order to have this done from any connection but I have not tested this final part.