is Walt Disney considered an artist?

He IS "considered" dead, but popular gossip has him frozen in a vault beneath Epcot Center at Disney World.

He WAS a cartoonist and fair sketch artist. It is known, however, that many of the cartoon charaters used for his films were actually draw by his good friend and associate, Ub Iwerks. I'd say that Disney probablly drew some prototype characters that Iwerks developed further for use in the films. You can see a HUGE difference in the Mickey Mouse from the Steamboat Willie era and the more modern looking Micky of later years. Ub Iwerks probably is the one to "modernize" the character.

He was a successful cartoonist with training as a fine sketch artist.

Short answer, yes. Longer answer, he became a commercial artist (therefore provable) in 1919.