I ALWAYS say hello as the first thing in any chats that have some kind of importance. Why? because the person may be presenting to 200 people and my message will be displayed. They may be with someone and they cannot communicate. If this is a message of the kind "lunch at 12?" then fine, but anything remotely sensitive starts with hello, and I wait for that person to respond.
It's fine to say Hello, as long as it's immediately followed by something consistent, preferably in the same message
And wait for the other person to reply, I then assume it is safe to chat.
This is obviously for more sensitive/professional settings but directly saying "we have had a 100M loss because of that M&A", even on a safe IM, is irresponsible because this is likely to pop up on their screen.