It seems that the "Hip Hop" entry is for the whole (sub)culture while the rap (aka hip hop music) entry is just for the music.
Just for the sake of clarity, maybe they could be renamed to "Hip Hop Culture", and "Rap Music" or "Rap/Hip Hop Music"?
(I'm not an expert either, so feel free to suggest better terms if such things exist.)
It's right that "Hip Hop" is the term for the whole (sub)culture which consists of different elements, especially Rap, DJing, Graffiti and Breakdancing.
So I think we should definetely have a credit for the whole culture. Either "Hip Hop" or "Hip Hop Culture" as mirva proposed.
Hip Hop music can be music whith rap but also instrumental music (without rap) played by a band or - more common - produced by a DJ/producer or beats with vocal samples and scratches by a DJ.
As "Rap Music" is always "Hip Hop Music", I think the broader term "Hip Hop Music" is okay.
A credit just for "Rap" or "Rapping" can be helpful for books/articles about the art of rapping (there are books about rhyming techniques, learning how to rap or write rap lyrics, the development of rapping in the history of music which has roots in Jamaican music and funk/soul,...). Also books which focus on specific MC's/Rappers should in my opinion be tagged with "Rap" (or "Rapper"?).
I hope this is helpful.
Thanks for the replies. i'll keep it as is then as it was an easy subject to find. I hadn't thought of the wider culture of hip-hop.
According to KRS-ONE:
Hiphop - consciousness
Hip Hop - culture
hip-hop - products