Hi Rob
A quick glance through JG 51's losses does not show any Emils, only Friedrichs, (predominately F-2) during Operation Barbarossa. However, at around February/March 1942 there do appear a couple of Bf 109 E-7 losses, including two flown by future RK holders Leutnant Joachim Brendel on 6 February 1942 and Leutnant Ernst Weismann on 20 March 1942. At
www.ww2.dk/air/jagd/jg51.htm you can see that there are a number of E-7 fighters listed on the Flugzeugbestand und Bewegungsmeldungen of I., II. and IV./JG 51 as of March 1942. I hope that this helps you out somewhat.
Horrido!
Leo