Both US and HKSAR passports holders can enroll in EasyPass. It does not appear GE is a requirement to enroll in EasyPass.
http://www.cbp.gov/global-entry/other-programs/easypass
To register for EasyPASS, U.S. citizens must visit an enrollment center operated by the German Federal Police in Germany. Enrollment centers for EasyPASS can be found in Terminal 1 at Frankfurt Airport and in Terminal 2 at Munich Airport. More enrollment centres will soon be available. To qualify, U.S. citizens must have an electronic passport (epassport), and be at least 18 years of age.
http://www.bundespolizei.de/EN/EasyP...Pass_node.html
EasyPASS-RTP PDF
EasyPASS-RTP is a registered travellers programme for non-EU-citizens. After registering at a Federal Police enrolment centre, holders of Hong Kong (HKSAR) or US electronic passports aged 18 years or older can also use the EasyPASS system for border checks. Enrolment centres will be located at all airports where EasyPASS is installed (see map below).
While enrollment, for now, is limited to FRA and MUC, it looks like EasyPass is available at those two airports as well as DUS and HAM.