How old are your Red Rock cross layers? If they are less than a year old, I would check to see how their egg size matches up to the ideal hatching egg size for the parent breeds of the cross. The reason why is because for the first few months of laying, pullets tend to lay smaller eggs which means any chicks hatched from those eggs have less room to grow, less nutrients to grow on, and have a higher mortality rate than chicks hatched from good sized eggs. Some people say wait until your hens are a year old, but that is only because they have usually gotten out of the "pullet egg" stage by then. Other than that, I don't see why hatching chicks from your hybrid crosses wouldn't work. Just make sure you are selecting clean, good sized (but not freakishly huge as that can be a risk of a twin chicks which causes problems when hatching), well formed eggs more round than bullet shaped and you should be good to go.
Another thing you can do to see if your rooster is getting the job done is to look for the embryo bullseye (you can find pictures and instructions online) when you are cooking to see if your eggs are fertile.
