The green is a known predator in the wild. And has shown this behavior in captivity. Is it true of all individuals? Definitely not.
The other brittle/serpentstars (there is no biological difference) are not KNOWN to be predators in the wild, but few have been studied. Other brittlestars have been reported to cause trouble, but what is unclear is this:
How often the are fed (and not allowed to scavenge)
The "health" of the animal they are assumed to have caught.
Many people accuse them of, frankly, outrageous things like "brittle killed my trigger/tang." Some are a threat to smaller fish and shrimp...but not all. And of those accounts of them catching stuff, I reckon many of the animals were dead and being "cleaned up" by the brittlestar.
So, avoid the green, and feed any others. But you assume a risk keeping any unnatural assortment of critters as we do in our tanks. We want the wild piece of nature, but don't like it when things follow instincts. I am sure for any "reef safe" critter such as shrimp and hermits, I could find people who said "it ate my ____________."
I keep many brittlestars. I would say without a doubt the greens are most aggressive. I have no indication that they have directly killed an otherwise healthy animal, but I would not recommend greens overall.
i have a black in color brittle star that i bought on swf(picture is under inverts on swf) and he arrive with only 1 full length leg and the rest were small and he is doing well the other legs are growing fast and i feed him small pieces of shrimp 1-2 times a week and he hasnt killed anything yet, he mostly just hids under my live rocks.