Yes, I'm aware, as I went to an HBCU myself and know each of the 5 options all attract different types of men. There are four other black fraternities that each better fit any version of Randall. Including a Sigma (which SKB is in real life).
No. They, in general, are rougher around the edges, seeping with self confidence, and very masculine. They are often (more than any other black frats) physically large men as well, they tower over others. If I were casting an Omega in a movie, Terry Crews would be my starting point. Omegas are also (stereotypically) the non-academic ones.
Not sure any black frat would be defined as assholes, but there is one that's known for having a hard time settling down because they are a tad cocky.