CPDs will eat shrimpletts that are just released but after a molt or two there shouldn't be an issue if there are plenty of hiding places and you keep them well fed. I have some in with my Taiwan red cherries and I still see healthy population increase. If you want higher shrimp survival rate then don't put them in with anything that will eat them and stick to a shrimp only set up.
If you're dead set on keeping the shrimp in a separate tank to grow out then add a heater, sponge filter, a big handful of java moss, and conditioned tap water . Change out 10-20% of the water weekly and feed them high quality food every other day. I've noticed my Blue velvets grow a little slower than the cherries but should be big enough not to get picked off in a couple of weeks.