See the official syllabus (posted on my webpage, about half way down). It says "application of Hund's rules to determination of magnetic ground states of isolated ions.". So yes, they are officially examinable. Note however there has never been a question on Hund's rules since about 2000 and I think it is therefore unlikely that they will appear. Note: In the older days pre-2000, it was a typical question to ask about Hund's rules in a solid -- in which case you have to worry about quenching of angular momentum. By saying "isolated ions" it means that this aspect is not examinable and many of the old exam questions would not be allowed.