Every nightly product build creates p2 repo which is literary the update site that can be used to update previously installed p2 enabled JBDS.
Example of location this p2 repo in build results is

http://reports.qa.atl.jboss.com/binaries/RHDS/builds/staging/devstudio-4.0_trunk.product/builds/nightly/trunk/201012260136/jbds-all-package/buildRepo

It should be published and available from static location so QA can use this URL to verify update. This URL could be

http://reports.qa.atl.jboss.com/binaries/RHDS/builds/staging/devstudio-4.0_trunk.product/updates/nightly/trunk