Same person, but ukimori is their twitter handle and a species they created while ultraviolet is the name they actually go by.
Granted, ukimori_(artist) is only used on one post that also already has the ultraviolet tag, but since I tried searching for ultraviolet using "ukimori" and that tag even exists its clear that others have as well and will continue to do so.
Also being unable to use the "request alias" feature because one tag has too few posts is kind of annoying.