unless you have evidence that this accelerator committed fraud, I'd probably hold off on directly accusing them of scamming. I'm not a lawyer, but that seems like dangerous legal territory.
It's perfectly legal to express your opinion that something is a scam. It's also legal to claim something is a scam based on your personal knowledge of a situation. It's only illegal (defamatory) to claim something is fraudulent if you know that it actually is not and are knowingly presenting false facts. IANAL, but I don't see how this post fails that test, unless the author is lying and knows it.