Who actually delivers Gatsby's eulogy at the funeral in The Great Gatsby?Why did Fitzgerald find it necessary to add this particular part into the story?
Technically speaking, it is Owl-Eyes. His statement of "The poor son-of-a-bitch" sums up Gatsby in a nutshell. His presence in the novel is almost that of a seer, as he has the power to see things more powerfully than others (just as the other bespectacled character in the book, T.J. Eckelberg sees the Valley of Ashes for what it really is). Owl-Eyes notices that the books in Gatsby's library are "absolutely real" (Chapter 3) and that "this fella's a regualar Belasco," a reference to David Belasco, a noted set-decorator of the 1920's. He understands that everything about Gatsby is smoke and mirrors, and he becomes the only person who sees through Gatsby enough and is detached enough to tell the truth about him. So, his judgment of Gatsby becomes an interesting juxtaposition to Nick's "You're worth the whole damn bunch put together."
The only other thing that I can think to add to this is the fact that Nick's final remarks act as a eulogy of sorts for Gatsby.
Gatsby believed in the green light, the orgastic future that year by year recedes before us. It eluded us then, but that’s no matter—to-morrow we will run faster, stretch out our arms farther. . . . And one fine morning——
So we beat on, boats against the current, borne back ceaselessly into the past.
In essence, this is Nick's eulogy for Gatsby. A eulogy does not have to be delivered at the funeral. It is generally a text of some sort (it can be a poem, even) that honors the dead. In this case, the entire novel is a eulogy as well, an extended honoring of Jat Gatz his one true friend, Nick Carraway.
So far as I can tell, there is no eulogy for Gatsby. If there is one, we do not hear it or even see any reference to it. All we know about the funeral is that Nick and Mr. Gatz and the minister, a few servants, the postman and Owl-eyes are there. We hear someone say something about how the dead that get rained on are blessed. We hear Owl-eyes say "amen." But we don't hear a eulogy.
I think that Fitzgerald wanted to show how empty Gatsby's life was. He is showing that all of Gatsby's material wealth, his American dream, did not get him anything in the way of relationships or love.