Star Trek: 10 Things You Didn’t Know About Wolf 359
4. The Klingons Are Coming
"The Klingons are sending warships," said Admiral Hanson over subspace in The Best of Both Worlds, Part II. Despite a lot of speculation and reasonable doubt from episodes such as Unity, there has been NO definitive on-screen evidence that the warriors ever made it to the Battle of Wolf 359. StarTrek.com's logic was once devastatingly simple: "[Hanson's armada] didn't last long enough for expected Klingon aid."
In Unity, it is certainly true that there were Klingons amongst the former Borg on the planet in the Nekrit Expanse. Add that to Riley Frazier's "[assimilation] at Wolf 359," there was a degree of correlation without probable causation. Chakotay's visions within the Cooperative neural link also contained footage of the Battle of Wolf 359 from Emissary, interspersed with shots of various Klingon ships (in fact re-edits from The Way of the Warrior). At best, that is only evidence the Klingons engaged the cube at some point on its way to Sector 001.
Outside of canon, others have been more optimistic, or pessimistic in the 'today's-not-necessarily-the-best-day-to-die' sense. For example, Ghosts, the tenth issue of the Marvel Star Trek: Voyager comic book series, published in 1997, depicts several Klingon ships — including at least two K't'inga class and one Vor'cha class — engaged at the Battle of Wolf 359.
In JTVFX's Wolf 359: The Massacre II trailer, multiple Klingon ships can be seen fighting alongside the Federation. Towards the end, the trailer even features (*spoiler alert*) Klingon General Korok, as seen in Unimatrix Zero and Unimatrix Zero, Part II. The character's time and place of assimilation are never specified in those episodes, however.