Here's the Oxford English Dictionary's entry on "evolutionism": 
 :The theory of evolution or development. 
 :1869 HUXLEY in Sci. Opin. 28 Apr. 487/1 The three schools of geological speculation which I have termed Catastrophism, Uniformitarianism, and Evolutionism. 1872 E. FRY in Spectator 21 Sept. 1201 Evolutionism does not propose to explain the unfolding of life out of dead matter. 1873 DAWSON Earth & Man xiv. 348 Evolutionism..excluded creation and theism. 

 A few other quotes: 

 :"Nothing can give a better idea (in small compass) of the growth of Evolutionism and its position at this time, than a quotation from Mr. Huxley* — " 
 (Francis Darwin, Life and Letters of Charles Darwin) 

 :"In France, the influence of Elie de Beaumont and of Flourens-the former of whom is said to have "damned himself to everlasting fame" by inventing the nickname of "la science moussante" for Evolutionism,* -to say nothing of the ill-will of other powerful members of the Institut, produced for a long time the effect of a conspiracy of silence; and many years passed before the Academy redeemed itself from the reproach that the name of Darwin was not to be found on the list of its members." 
 (Ibid) 

 :"It is satisfactory to hear so capable an anatomist, and so embittered an opponent of evolutionism, admitting even the  possibility of either of his first propositions." 
 (Charles Darwin, The Descent of Man) 

 I just came across those searching through the text on the British Library's collection of Darwin's works. What seems worth wondering to me is not whether the term was ever used, but whether the entry should 1. be about the term itself, and 2. whether or not the information currently on the page is just a duplicate of the article History of evolutionary thought. I am feeling that any useful information should be merged with the latter article and the Evolutionism article should be somewhat more devoted to the term, or redirect to the "history" article and have an entry at Wikitionary.