SP.UI controls does not work on provider-hosted apps
We recently had an issue while migrating an auto-hosted app to a provider hosted app. The people picker control would not work.
The issue arises as SP.UI namespace controls are not supported on provider-hosted apps.
“Unfortunately you cannot use the client people picker on a provider-hosted page. SP controls only work on SP hosted pages. The only control designed from the ground up to work on remotely hosted pages is the chrome control.”