You know I was thinking the same thing, but maybe its different between V8 and V6. On the V8, the catch can connects between the PVC valve and intake manifold, no where near the air filter. There is a so called air makeup hose connected from the crankcase to the air filter box, but air should be flowing from the box into the crankcase, not into the air box. Oil on the air filter is probably blow by (either the PVC hose is blocked or valve defective or you have serious ring problems).
Are others seeing a lot of oil in the V6 air filter housing?
Current: 2011 Grand Cherokee Overland V8, 2009 Liberty Rocky Mt V6
Previous: 2000 Grand Cherokee Laredo I6, 1979 CJ7 I6 Quadratrac