If all bootcamps were closed down, would it make any difference at all to SWE employers?

Yeah, but maybe a caveat is that this is at bona-fide "tech" companies. Ask any eng manager and they'll tell you that internships and juniors are ,on average, net-negative financially, and the main goal is to turn them into super mid-level and senior engineers. This doesn't apply to non-"tech" companies (it does to some but not as strong), where you are expected to have a skillset coming in and then are deploying that skillset on day one, for example, agencies, contracting companies, tech-adjacent companies (like healthcare or financial companies).