They can, but you will cause a lot of fighting. Everytime you introduce birds to an established flock, you cause hen pecking and stress. As meat birds would not have have a long life anyway, it is alot of stress on your layers.
I've raised a small batch ( I think there were less than 10) of CX in with my layers and they did fine. They were so young and so non-threatening to the older hens, they were mostly ignored. I did free range my birds at that time, so the hens weren't closed in with the meaties and I think that helped quite a bit. I think space and weather is going to be your deal breaker here. If your birds are already crowded for space, don't do it. If the weather is bad and the hens are spending most of the day in the coop, don't do it. If you're talking about in the spring, you've got lots of space to put multiple feeders and waterers, hiding places for the little piggies, the hens get to range or spend most of the day out in the run, you could give it a try. Just be prepared to do a big coop clean out after you process the meaties, they will challenge even the best deep litter system.
My flock(s) are fluid enough adding or moving birds doesn't seem to stress them, mine are used to it. I've got broodies raising chicks, I'm putting incubator/brooded chicks in the pens, pulling cockerels to a grow out pen, etc. The amount of stress will depend on what your birds are used to.
I feed everyone an all-in-one, even my meaties. When I do some this year I may use broiler feed for them and see if it makes a difference. I can get the all in one in a bulk tote for a discounted price, so another week or so isn't a big deal for me, still cheaper than broiler rations by the sack.