In a tank that large they could easily hide out.But depending on your fish they may also be seen as tasty snacks.I keep them in all my tanks,even with my fantail and my crayfish.They get eaten now and then but I kind of expect it.
Ghost shrimp are sold as food here. Last time I had some they really didnt like my tank temp, and rapidly died. When I had them before they got eaten and a few died (don't know why), however one of them survived and did so for about 5 months.
I dont know why they are hard to find up here in Canada where I live but they are always sold out when I get there and they are $2 each.... yes each!!!! I am jealous of all of you who get them so cheap
The only place that sells them around here is walmart, and they want 24 cents each. I can't imagine paying 2 dollars for one when I wouldn't expect them all to survive in my tanks.