Should we be looking at Slack as an example here? Their interface is necessary for people to use it, if your company uses Slack you will have to use their UI/UX. Whereas for AWS, your engineers are more likely to make the call on UI/UX, and not the executives.

Are your executives launching servers? Do they care about their IDE's UI too?

I disagree with this, in my opinion slack has a lot of features on top of IRC (offline messages, webhooks, etc) that make it much more usable for its target audience.