It's common when corps buy large enough companies that they don't want to kill the original brand. That's why you get hotels like "(something) by Hilton".

Do you mean Red Hat identifies itself using the phrase "Red Hat, an IBM Company"? Because I don't see any use of this on redhat.com (including that website's corporate "about" content) and if any Red Hatters are using this phrasing (I'm a current Red Hat employee) I haven't been aware of it.

I have seen it in several articles. (I don’t work for HashiCorp or Red Hat subsidiaries so no idea what is said or done inside those subs)

1. https://business.adobe.com/customer-success-stories/red-hat....

2. https://www.openpr.com/news/4100338/linux-operating-system-m...

You said "It’s how Red Hat identifies themselves too" but those two articles are not by Red Hat. So ... it's not how Red Hat identifies themselves, though it seems to be how Hashicorp identifies themselves.