I have never came across any references to the Gatling gun being used on the Western front, but I was interested if any surplus Gatling guns ever made their way to action in other fronts, such as in Africa, Middle East, etc. I've recently become very interested in World War I, and it seems that, although technologically inferior, the weapon could still have been used with devastating effects in areas that did not have the proper access to 'then' modern day machine guns.
In a rare example from the heart of the Western Front a solitary Gatling gun was used on a turret of Fort Manonviller in France, protecting the Franco-German border. Originally built in the 1800s and considered obsolete in the 1880s, the fortress was occupied a strategically important position and was modernised in the 1890s, with the Gatling gun added in 1896 to support two larger guns.
There are accounts of turrets being prepped for Gatling guns in the flurry of fortifications that sprang up in the aftermath of the Franco-Prussian War, but only Fort Manonviller received one - something of an 'experimental' arrangement.
Fort Manonviller was first attacked by the Germans on 8 August 1914, and held out until 27 August - it had been isolated and surrounded for four days and subject to a masterclass in German siege artillery for 52 hours.
One would assume - or perhaps hope - that its lonely Gatling gun made a good account of itself.
Sources: Breaking the Fortress Line 1914 by Clayton Donnell, 42cm “Big Bertha” and German Siege Artillery of World War I by Marc Romanych and Martin Rupp, and Verdun 1916: The Deadliest Battle of the First World War by William F Buckingham