I feel like I've seen something similar as a general rule. If your company has any sort of internal etiquette guide for its internal communication tools, this should go there verbatim. If not, then it can still work to post it in certain places; for example, a slack channel where people ask your team questions.
If you're getting asked questions but your teammates aren't, then you are special! So just tell them directly. Even better, respond to the DM saying that for the benefit of everyone, such questions should be asked and answered in a public channel, so that others have a fighting chance of finding it with a search tool. This eliminates the "hi" problem entirely.
However, Bob pretends to be afraid of me. People walk up to me all the time when I'm working and ask questions and it's perfectly fine. But when Bob has a question, he _whispers_ to get my attention. Or he'll stand just in the periphery of my vision and literally wave until I respond. I've told him, nicely, more than once, that he can just talk to me whenever he wants. His response is always along the lines of, "well I didn't want to break your concentration" or, "I didn't want to bother you if were busy." Bob knows I don't ignore people whether I'm busy or not. I don't want to believe he does it just to annoy me but I'm failing to come up with a more logical explanation.
Improving this style of interaction may be a matter of showing/proving that you really don't mind a more blunt approach, and in fact prefer it.
I've been trying to think of a good way of asking it. Maybe something like "Just so you know, I won't be offended if you ask the question with your initial greeting. It would actually be helpful because then I can start thinking about the answer right away. :)" Does that work?
If they say "Hi" and wait for you to respond, now you're engaged and it's harder to ignore after they pose the question.
To carry your analogy further, it's more like calling someone and hanging up before they answer in order to prompt them to call back.
I am saying "Hi" (without anything else) - to check if person is available for discussion (exactly like okusername described it).
What feels demanding to me is coworkers who will simply send a message containing my name, sometimes followed by a period. Opening slack to see just "John." (not my actual name) is somehow both more and less personal than "Hi". I believe it's mostly a language barrier thing, as it's only ever ESL speakers who do it, but it still feels like nails on a chalkboard for me.
Here it is: "please don't just type "hi"". It's that simple. I've never had anyone perceive that as rude or negative in any way, and they usually adapt pretty quickly. If they don't learn, you just have to step up your ignoring game ;)