When using Environment Manager policy (ADMX action) to set a Group Policy Object (GPO) to manage the screensaver settings specifically in XenDesktop 7.0 & 7.1 the policy updates the relevant values within the registry on the endpoint, however the GPO does not actually apply for users as expected. The same policy works as expected on XenDesktop 4.5.
This behaviour is caused by changes in XenDesktop between versions 4.5 and 7.0.
Environment Manager working as expected and is applying the registry settings as intended. The problem here is that there is an additional registry value that is required to be updated. This registry value & further detail surrounding this issue can be found on the Citrix Knowledgebase. See the references section below for the relevant hyperlink.
You will need to edit the registry and create the following:
Registry Key: HKLM\Software\Citrix\Graphics\
Value Name: SetDisplayRequiredMode
Value Type: DWORD
Value Data: 0
This change does not prevent the remote machine screen saver or power save mode from coming on. If the power save mode comes on, the remote session is not updated until the user provides input (mouse/keyboard), but the screen will not be blanked.
Screen savers and the power-save option are disabled in XenDesktop sessions by default. See the the Citrix Knowledgebase article for further detailed information: