There isn’t a species of freshwater shrimp that eat one another while living. The cases you read over the internet are people finding their shrimp devouring one by either: a very sick (brink of death) or dead shrimp. I personally house Amano Shrimp with RCS and never once seen them eat a fry.
The only minor problem would be a little bullying once in awhile if you feed them with a dish. (Amano Shrimp are 5x the size of RCS, glass are about 2-3x)
People jump to conclusions with what they “see” - shrimp fry die all the time, typically a 10-20% kill off from fry to adult. So when hobbyist sees a RCS chowing down on another shrimp carcass, they instinctively think it was killed by another shrimp. Where-as it might of died from starvation, failure to molt, disease, bad conditions, act of god, etc etc.
Well why do shrimp eat their dead relatives? Well to get valuable minerals. They are a scavenging species - they will molt then eat their own exoskeleton to retain as much nutrients as possible. So for them to eat their own kind, it’s not uncommon. Where a shrimp carcass can dissolve within the water in less than 48 hours (with nothing eating it).
So to rap it up, don’t worry about interspecies of shrimp. Clean-up crews in varieties are nice. They typically pair themselves off as well, which is very interesting to watch.