A couple of standard solutions/suggestions. Is your HANA Studio installed into a sub-directory your program files directory? If so, be sure to run the HANA Studio with Windows Administrative privileges otherwise the standard eclipse Update Site will be missing. This might explain the missing dependency. If this is the case, you can add the update site manually. Its http://download.eclipse.org/releases/kepler
Also what update sites are you trying to install ABAP/UI5 from? Is it the public site: tools.hana.ondemand.com
If so there was version change to the underlying Eclipse in HANA Studio. You want to change your update sites from Juno (https://tools.hana.ondemand.com/juno) to Kepler (https://tools.hana.ondemand.com/kepler).