IMO, out of privacy concerns, do not use your personal Apple ID on United's iPad. From Flying Together, to turn off the Apple ID request,

"Find My iPad. iOS 7 features an iCloud feature called Find My iPad associated with your Apple ID/iCloud account and password. Please ensure that this feature is turned OFF on the company-issued iPad EFB. If turned ON, you will need to provide your Apple ID and Password should your device ever be lost, stolen or returned."

Use the "United iPad Guide — Configure | Enrollment | Reset | Setup" at Flying Together and it shouldn't ask for the Apple ID.