If youre talking about yellow star polyps as something related to GSP and Briareum, then they dont really sting per se, but they are exceptionally toxic, and can damage corals around them (especially stony corals). They are also very capable of just overrunning any coral/object around them and smothering it out of existance.
If you are talking about the yellow "Parazoanthus" polyps, they still dont really sting, but can irritate stony corals if close to them. They dont reproduce nearly as quickly as the one detailed above, but can still cause a problem in the long run.