Yasha's are probably like the highfin red stripes: THOSE two might not mix, but the highfins are pretty accepting of tailspot blennies, Yellow watchmen, firefish, and chromis. Their whole desire is to live apart and not hassle anybody. A bit delicate, but well worth the effort. The highfins eat cyclopeeze.
I agree with the statement: not sure about the sleeper. It's more likely to bluster, like the ywg, and just declare its territory, which the yashas are pretty well going to respect. Note: they're not large.