ADF??? you mean that silly thing with a needle that doesn't know where to point to when:
-You are turning
-It's raining
-There's CBs or thunderstorms around
-You are flying at night
-You are flying near the coast
-When you are on certain headings
Yeah still a handful of JAA members who stipulate an ADF to be installed in order to be certified for IFR. If you want an exact answer you'll need to trawl through each one's AIP. There's normally a section for 'IFR min requirements'.