If they are actually fan made, introduced to Oda by a SBS and then introduced by Oda himself into the manga then imo you can consider them canon but they will not have any relevant part in the story, most likely, even because Oda has barely time to fit in admirals, VA, gorosei, holy knights and what not.
What I think may happen is the introduction of a 6th and final admiral. The 3 original admirals have the 3 primary colors: red, blue and yellow, now red got promoted and violet was the new admiral while blue was kicked out and green replaced him. Now we just need yellow to somewhat cease to be an admiral and have orange take his place. Somebody who knows more than me here thinks it should be orange mouse or something like that (following a chinese or japanese zodiac the other admirals nicknames are based upon). But at least it is to be expected to complete the secondary colors after the primary ones (even if the time to introduce new characters is long gone, even worse when you have gorosei fighters, Figarland and holy knights to introduce).