Pink elephants have been used before the Disney movie.
Looking at the Corpus of Historical American, I find the following sentences.
I'm just as cordial a friend as whiskey ever had; but my con science rebels at floodin' my vital organs with seventeen different colored wines at one meal. I've been infested with pink elephants an' green dragons an' I never com plained none; but hang me if I can get any comfort out of a striped yellow spider ten feet high on horrid hairy legs.-- Wason, Robert Alexander (Happy Hawkins, 1909).
"You'll see me! You've been usin' me and my schooner long enough, and if there's anything in this yarn of yours, it's mine. Who's this man?" "He's a rich man, and he'll take us," said Dinshaw. "I'd believe ye sooner if ye said ye saw pink elephants," said Jarrow. "Git down to cases. What's his name? " "Money talks," suggested Vanderzee. " Moonshine! " declared Peth.-- Moore, Frederick Ferdinand (Isle o' Dreams, 1913)
All I could see were strange faces bobbing around that at times looked like pink elephants and Kodiak bears. One with the headdress of the Sisters of St. Ann seemed kindly, and I was prevailed to follow her to the hospital. She was Sister Epiphane, the trained nurse. She plastered me up with antiphlogistin mud and off I went to bed.-- Hubard, Bernard R. (MUSH, YOU MALEMUTES!, 1932)