When I think of "composer" I think of a more classical sense of music and someone who writes music so that others can perform it. That's what music theory leads to and writing music, you compose a piece of music with musical notation in mind. Yes, "compose" can mean to compile or bring together a final product, but for me, personally, being a "composer" is more geared to traditional music writing. However, someone who creates an original composition is technically a composer and that can't be denied.
Beat-making or being a beatmaker to me is the most safe term because that is what is happening: a person makes a beat. That can mean it is originally composed or it uses samples. It is a BEAT, a hip hop or rap beat and someone MADE it.
Producer can be either way: you produced (created) a beat or you produced a track that includes being there to make sure a vocalist delivers the goods. Producing in the beat-making world is synonymous with being a "beatmaker" if you ask me.
It seems that a lot of it has to do with how the rap and hip hop world perceives these terms because everyone will be on the same wavelength. If you notice, a lot of people say "Producer" or "Beatmaker." Not a lot of people are saying "Composer" and that is for a reason. It could be marketing reasons or just that "composer" doesn't fit. A hip hop producer isn't probably going to call themselves a composer in 2011. They want to market themselves as a "Hitmaker," "Producer," or "Beatmaker." I think that "Producer" is most common.
Especially when in credits you see "Produced By:."