The answer depends on just when you are talking about. The existence of German AI radar detectors proves the Germans were aware of AI radar; several are documented in various wiki pages: for Metox (in 1942, by U-boats), Naxos (1943, by U-boats and aircraft) and Flensburg (1944, by aircraft). These make it clear that for the second half of the war the answer was "yes".
[Thanks to @rs.29 for the Naxos cite.]
A fun read covering this is R.V. Jones Most Secret War (or in the US, Wizard War). The Wikipedia articles cite Brown, Louis (1999). A Radar History of World War II: Technical and Military Imperatives, which is less fun but still packed with info.