"Was machen sie?" simply means
What are they doing?
And "Was machen Sie?" means
What are you doing?
Note the difference between "sie" (they) and "Sie" (you).
Side note: "Was macht sie?" (verb in singular form) means "What is she doing?"
There is absolutely no greeting connotation in those questions. It would be very impolite to enter a room and ask this question without greeting. Asking this question means to demand accountability.
But there are questions that contain greeting connotations:
Wie geht es dir?
Wie geht es Ihnen?
(often "geht's" instead of "geht es", i.e. "Wie geht's dir?")
How are you?
But in the German question the greeting connotation is weaker than in the English sentence. So, you more often will hear an explicit greeting before this question:
Servus, wie geht es dir?
Guten Abend, wie geht es Ihnen?
Reaction to a comment:
If someone asks you "Wie geht es dir/Ihnen?" your response should be an answer to this question, not another question! The standard answer is to say "thank you" (for being asked) and then you say, that you're fine. Then you ask the same question. Then it's the first person's task to say "thank you I'm fine".
Walter and Irene meet at the bus station. They are colleagues, working together in the same office (so they use "du" instead of "Sie"), and they live in the south of the german speaking area (so their preferred greeting phrase is "Servus").
Walter: Servus, wie geht's dir?
Irene: Servus, danke gut, und dir?
Walter: Danke, auch gut.
Walter: Hello, how are you?
Irene: Hello, thank you, I'm fine, how are you?
Walter: Thank you, I'm fine too.
Frau Müller is owner of a little grocery, Herr Jäger is one of her customers (so they use "Sie", not "du"), and they live in northern regions (so their preferred greeting phrase is "Guten Tag"), and they meet at a bus station too.
Frau Müller: Guten Tag, wie geht es Ihnen?
Herr Jäger: Guten Tag, danke gut, und Ihnen?
Frau Müller: Danke, auch gut.
The translation is the same dialogue as above, just with other names.