JGr. 200 was equipped with worn out Bf 109 G-6 that had served in a training unit (JGr. 200 was activated in June 1944 from among the instructors and better pupils). Several of its aircraft had a 3 cm cannon firing through the propeller boss. The second Staffel was equipped with the WGr. 21 mortar but I only have evidence for these being used air-to-ground, not air-to-air.
Go to
http://www.ghostbombers.com
Click on the "Operation Dragoon" link and page through the section "Before D-Day" for more about JG 200.
I think the hardcore fighter junkies on this forum may be able to tell you something about Isken's earlier career.