The green brittlestar is a known predator in the wild - certainly a risk but by no means certain to eat anything. Others are hit or miss, IMO, and feeding won't always help. I don't have any issues to report personally, and I have 11 brittlestars.
There is no difference, BTW, between brittlestars and serpentstars.
And no, it is not a threat to the chocolate chip star for sure.