Chances are VERY good.
I have four mixed-breed bantams co-parenting about 20 chicks right now. All of the chicks they hatched out are about 2 weeks old. But MANY of the chicks in that little flock also came from the incubator (it's cheaper to use a broody hen than a brooder lamp!)
Yesterday I had a new one hatch - by itself. It's a large-fowl ameraucana, so it's about the same size as the bantam chicks right now. I made sure to wait until he was standing steady before putting him outside, so at least he could run to catch up as the others moved around.
WellI JUST set the new chick outside before typing this out and watched for a while. The mommies wanted to peck at him at first, but when they realized he just hunkered down and didn't know what to do about it, they seemed to understand he was just another baby, and stopped pecking at him. Finally the hen that is currently leading the silkies around let him lightly peck HER face - and then puffed up and ran at ME when I reached down to touch him again! I knew right then that he had been successfully adopted!
I really wanted to mix this chick with the hens because he's another "lone hatch" meaning he wasn't hatched near the same time as any other chick. The hens will not only protect him and keep him company, but they'll also keep the other chicks from pecking on him too. While the bantam chicks are about his size, the hens are fostering some large fowl that are bigger, and I didn't want to run into those problems. But the mix has been successful.
And better yet - I didn't have to wait until night time when they were all piled up in the nest to sneak him under the mommies! That was going to be my alternative choice if they didn't accept him just now. But they did, and problem solved
