Yes, you can do unattended (or silent) installs from iOS 7 onwards on supervised devices. For iOS 6, the user will see the install/cancel prompt and unattended installs without user intervention is not possible.
From Apple Launches "Managed Distribution" for App Store Volume Purchase Program (VPP) for Business and Education (Submitted by Aaron Freimark on November 4, 2013 - 11:08pm):
Apple tonight updated its app Volume Purchase Program with several long-anticipated and important additions. The updates introduce a new "managed distribution" of apps to iOS 7 devices, allowing assignment and revocation' through Mobile Device Management.
Assigned apps are installed automatically on supervised devices. Unsupervised devices show a prompt to install.
From iOS 7: What it means for Enterprise, Education, and Government (
By Craig Johnston, Thursday, Sep 19, 2013 a 11:16 am )
With iOS 7 the following has been added:
Silent app installation. Now via the MDM API, an IT administrator can send an app to the device and have it installed silently in the
background. There is no need to ask the user which delays compliance,
the app just installs itself. This works both for apps in the iTunes
App Store that the company may have purchased a volume license for and
apps developed by the company itself for internal use, that are not
stored in the iTunes App Store.
Contrast this with what iOS 6 provides (described in the same article), which is (italics mine):
In iOS 6, through the use of MDM APIs you could:
Install Apps via MDM. This feature tells the user that they must install an app. The user could ignore this message and the
administrator will have to decide how to handle this. They could set
the MDM system to automatically lock their device out until they
install the app. They could keep calling the user asking them to
install the app. Either way, the app cannot be installed for the user
by the IT team.