Can someone have a creative disposition?
A disposition is usually regarded as similar to attitude. So, someone may have a surly disposition, or a happy disposition, etc. However, the word disposition, used in this context, would mean “something one is disposed to do”. So, if one were said to have a creative disposition, he/she would be disposed to (apt to, liable to, inclined to) be creative. So, to answer your question, I think that, although this is not the “common” usage of the word, it is an acceptable usage. Some other ways of saying this might be “has a creative nature”, or “has an inclination to be creative”, or “has a propensity towards creativity”. Hope this helps!