Yes, lots of people do that. As long as they have oyster shell.
But you might want to post this in the feeding and watering your flock section instead of random ramblings. You’ll get more help. A mod can move it for you.
There is no need to give oyster shells to chicks. Don't give oyster shells to chickens without good reason--like when you know that your chickens need additional calcium in their diet. It shouldn't be given until they're at 18 weeks old, at the earliest.
Are you talking about adult laying hens? If so, yes that is fine. As long as they have access to the oyster shell. Lots of folk feed starter/grower or all flock feed with free choice oyster shell on the side. See how your birds are doing, and adjust accordingly.