My reading of apple id's is one apple id per device for shared devices. For devices exclusively used by one individual, the user can have several devices on the apple id.
Anyway, you need to get an mdm. To prevent users from setting the activation lock, you need to supervise the device. There are two ways of doing this:
1) Use apple configurator.
2) Buy the devices through the DEP.
How to check if the activation lock is active on a device
https://www.icloud.com/activationlock/
When an employee check out an ipad, have them sign a note that they will be docked the cost of the ipad from their last paycheck if they do not turn in the ipad and deactivate the activation lock.
"This document offers guidance on some important considerations for getting the most out of your iOS deployment." Covers: Prepare your infrastructure. Set up devices. Configure and manage devices. Deploy apps and content. Plan for support.
https://www.apple.com/business/docs/iOS_Enterprise_Deployment_Overview.pdf
Quick overview of zero touch deplayment
http://www.apple.com/education/it/dep/
Consider DEP, Device Enrollment Program. Use VPP, Volume Purchase Program. Select an MDM, Mobile Device Management.
Overview of ipad & iphone deployment.
It's education focused.
http://www.apple.com/education/it/
Writing you own app for your business:
https://developer.apple.com/enterprise/
MDM -- Mobile Device Management
https://developer.apple.com/videos/play/wwdc2015-301/
For a comparison see this page:
http://www.enterpriseios.com/wiki/Comparison_MDM_Providers
VPP -- Volume Purchase Program
http://www.apple.com/business/vpp/
http://www.apple.com/education/it/vpp/
