In general, it shouldn't matter too much if one distro takes market share from another: both rely on a healthy kernel for their business and have motivation to continue investing. If distro B takes business from distro A then it has more revenue to spend on kernel devs and greater motivation to do so.
However, there is one competitor of RedHat (incidentally, the one whose distro is most closely related) who also owns a competing Unix implementation. They have less motivation to invest in Linux over their own product (let's call it Solaris). If a weakened RedHat led to less investment in Linux it would only help Solaris' competitive position.
I do have quite a lot of sympathy for RedHat in this position.