General Hux is a high ranking officer of The First Order. Kylo Ren is a member of the Knights of Ren, a group that appears to be a smaller faction within The First Order. On paper, that should make General Hux and Kylo Ren allies but what makes sense on paper sometimes doesn't translate fully when individual goals and personalities are factored. Is such the case with Ren and Hux. Domnhall Gleeson stated, "He’s kind of opposite Kylo Ren. They have their own relationship, which is individual and unusual. One of them is strong in different ways than the other. They’re both vying for power."
In the Force Awakens it appears that the Jedi numbers are not what they used to be. In fact, it's quite possible that Luke Skywalker might be the last Jedi in the Galaxy. But perhaps the Sith order is just as starved for members. Could the Knights of Ren be the last remnants of the Sith? Could the First Order blame the Empire's failure on having Force wielders at the top of leadership? All important questions that have miraculously remained a mystery through filming and marketing for The Force Awakens. However, we'll all get answers on December 18th, when Episode VII is released in North American theaters.