As an indie radio guy, I'm a little biased towards independent music platforms that accept submissions and demos versus more commercial routes. In my experience, indie, public, and community radio stations are consistently more supportive and beneficial for reaching the right audience for your music than any other media outlet.
For hip-hop artists, the same criteria and methods of promoting your music are true as those in any other genre. What is specific to you is that hip-hop has historically been a music style that celebrates the underdogs who rise to the top, as opposed to genres like rock or pop that tend to celebrate the celebrity image of success. The rags-to-riches story is pervasive in hip-hop, with icons like Biggy, Tupac, Jay-Z, Eminem, Run DMC, and so many more surviving a rough path to find monumental success through music.
Many emerging up-and-comers like to compare their talents to these rap legends, but what helped them rise to the top was their hustle and the ways they sought out getting their music into the hands of people who would support and grow their names. This is a short list of the hip-hop stations and programs I'd recommend, in seeing how they promote indie artists and hearing their programming.