I recently talked at length with someone who had just finished one of these programs, and learned that they do an incredible amount of "teaching to the test". That is to say, they very specifically and intentionally designed the program to teach people the things that are typically discussed during interviews. The number one goal didn't seem to be teaching programming or software engineering so much as teaching you how to pass the interview to get a job as a developer.
That said, the person I spoke to had created a project similar in scope and quality to what I'd expect a CS undergrad to do as a class project, and clearly had the ability to get things done. I'd guess someone from such a program could be a good developer, but with big gaps in understanding beneath the surface ability to do Rails or Node.JS or whatever the bootcamp used. If you're only doing html/css/javascript then the coding school is probably a sufficient education to get a web dev/design job.