Could be, though I know I’ve seen it in racial contexts before…or, at the very least, as suggestive of monkeys. Let’s see what Google’s got:
Merriam-Webster defines “gibber” as “to speak rapidly, inarticulately, and often foolishly,” and “jabber” as “to speak rapidly, indisctinctly, or unintelligibly.”
There are forty hits on Google for the phrase “gibbering ape.”
This website refers to “Simian jibber-jabber” when talking about monkey (sic) speech.
I don’t know what this page is, but it talks about “monkeys…jibbering, jabbering a song.” The song itself includes the phrase “Oh we clever monkey fellows with our jibber jabber ju.”
This appears, strangely, to be a story about the appendix. Here’s a couple sentences from it: “A long time ago, a million years BC … somewhere in the backstreets of the Amazonian rain forests, there lived a colony of monkeys. Thousands and thousands of them. All day long they jibber-jabber jibber-jabbered, threw coconuts at each other, and slipped around on their used banana skins.”
The September 15, 2001 entry of this WebJournal (I know, I know) is entitled “Crazy Monkey Jibber Jabber.”
This article talks about how most chimps “[jabber] incoherently.”
This one compares the “bickerings of Foreign Ministers” to “the jabbering on Monkey Hill.”
A section on this webpage is entitled, “News from the Jabbering Monkey.”
Here’s a passage from H.G. Wells: “The Monkey-man bored me, however; he assumed, on the strength of his five digits, that he was my equal, and was for ever jabbering at me,–jabbering the most arrant nonsense.”
This review of a solitaire game on the PCWorld website refers to “jabbering, comical apes.”
According to this art review, “[t]he Hindu symbol for the human mind is the jabbering monkey.”
Patrick McGoohan uses the phrase, “jeering and jabbering like a monkey.”
PrimateStore.com (“Everything for Primate Lovers”) pushes a plush squirrel monkey doll: “Antuco loves to gossip about the other monkeys, jabbering all day long about this one or that.”
From this page: “The monkey had ceased its defiant jabbering.”
On an episode of the X-Files, Detective John Munch (God love 'im) has the line, “Mulder? Is currently being held under five-point restraints and jabbering like a monkey.”
That’s enough to show, I think, that the association is at least somewhat common parlance. My apologies if LongRoad did not in fact have this comparison in mind, but, given his context, I thought of it immediately.