For crying out loud, stop turning this into your blogFAQs about policies related to real life tipping with real people, and someone just answer the question about whether sinking virtual money into a virtual tip to pay an NPC who needs no food or shelter rewards the player in some tangible way.
How is anybody supposed to answer?
Here's what we know: Tipping has no obvious effect.
That's it. Is there a hidden, more subtle effect? Maybe, who knows?