Well, mixing stingers with SPS is not a good idea in the eyes of many SPS farmers... I'll tell you why. SPS are more suceptible to the sting of softies or LPS. When they get stung, they are good enough dead. Vs. softies or LPS, that it takes a couple of shots to rid of them, it doesn't take a lot to kill an SPS piece since they are so darn sensitive. I have a mix in my new reef, SPS, LPS and softies. I am only limiting myself to one frag of shrooms and that's it, the rest will be complete stonies. My LPS consist of more docile, peaceful inhabitants like Acanthastrea genus of corals and Blastomussa pieces. The rest are Acros and Monti's. The Hillae and Echinata species tend to be asses, but as long as they are kept atleast 1.5in away from corals, they should not be able to reach. Although Hillae tends to spiderweb quite far. 
As long as you maintain a distance between them and like Amcarrig said, run carbon constantly and change it frequently, you can avoid toxins in the water released by soft corals. Also, you have to also take into account the spread of softies, as they do spread quicker than any stony in nature, they will outgrow the stonies and sting. 
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30g reef tank, CPR CY192 filter w/ DIY plumb running Rio 17HF return, Coralife 3x 9w UV Sterilizer, 3 24W T5-Helios 10K Daylights/3 24W T5-Helios Blue lights, 2 Logysis blue meteor light strobes (moonlights/24 Blue LEDs).
Tiger tail cuke, asst. snails/hermits, asst. feathers, rainbow acan,zoos,shrooms,bubble,galaxea, asst. shrimp, 2 ocellaris,mandarin,zebrasoma xanthurum,pink-spot watchman,red-striped pistol. | 
If you want to see the list of my corals, click the link in my signature below. 
