It is the mark of an educated mind to be able to entertain a thought without accepting it. The English adjective creationary is a natural derivative of the noun creation. It is true that the adjective is, at present, rarely used by English speakers and writers.
Most people are simply unaware of the adjective's existence as a legitimate word.
This is probably its chief shortcoming, but this situation is correctable. I believe that many or even most fair-minded evolutionists and creationists would be willing to use the word if only they knew of its existence and usefulness. Creationary, as an adjective, is exactly parallel to the corresponding adjective evolutionary. It fully conforms to the rules of English morphology or word formation. The meaning of the term is very important, especially for perceptive speakers and writers who are engaged in the creation-evolution debate.