I am Company A trying to sell an iPad app to Company B. Company B currently has 4 people. I have gave a fixed price for the app for enough licenses to fit the needs of his company. Five questions:
Would it be allowed for me to get a regular developer account under the name of Company B and distribute the app Ad hoc style (1)?
If not, would it be better to get into the Enterprise Developer Program under Company B and distribute the app that way (2)?
And what about the Volume Purchasing Program? I would build the app under Company A's Developer Program and then sell it to Company B. I would sell it for $9.99 but still get the fixed price (possibly minus the $9.99 x 4). Is that allowed (4)?
If Company A and Company B now want to cooperate and sell the iPad app to other Companies C, D, ... what would be the best setup (5)?
For more details on distribution methods, I find this useful (though a bit out of date with the latest changes to Testflight): http://mobiledan.net/2012/03/02/5-options-for-distributing-ios-apps-to-a-limited-audience-legally/
In answer to your question, I would sum it up with the following:
Yes, you can distribute ad-hoc, but depending on the method, your app can expire in 30 days (Apple Testflight, limit 1000 users), or 1 year (Diawi with provisioning profile, limit 100 users). https://developer.apple.com/testflight/
Enterprise: distribute to limited users by giving them a link, but they must all be part of your company. Apps do not need to pass any Apple Validation. https://developer.apple.com/programs/ios/enterprise/
B2B: distribute to limited users by inviting their emails. The users also need to sign up for Volume Purchasing, but they do not need to be part of your firm. However, apps do need to pass Apple validation. https://developer.apple.com/programs/volume/
A B2B solution sounds like it is the best fit for your scenario, and you'll also be able to adjust the prices to sell to other companies as you see fit.