this comes from a guy who has played table tennis and badminton extensively.
It depends on your priority. If everything is just for fun, then who cares
but if you try to be competitive in tennis, then the answer is depends.
The pluses - cross training will give you a fresh perspective on certain shots... I am sure you will be so good at the 'squash' shot - stretch fh slice.... also, I believe the bh slapping motion in racketball will help you understanding the tennis slice better (if you have problem with that shot).... I have actually used badminton rackets and shuttle to help people getting rid of the chopping motion in the tennis slice, because when they see the shuttle, they realize it's silly trying to chop it.
The minuses - it may get you wristy habbits which is no good for tennis... also because the racketball racket is much shorter, when you play tennis you will tend to hit low on the stringbed.... it usually takes 2-3 days for me to switch from table tennis to tennis.
but generally speaking, non of these bad habbits are permanent, but the pluses are... you understand that the tennis slice is a 'slap' or a push, not a chop.... and cross training certainly helps your footwork a lot, which is a permanent skill in tennis.