Should there? I mean, yeah, artists are gonna do what they want, but didn't Cygames and the horse owners ask not to lewd the uma?
First of all, why should anyone care if a company said no lewds?
Second, people completely misunderstand why Cygames even added that clause to their ToS.
The "no NSFW art" clause happened because a schizo sent eroguro art to one of the horse's owners, I forget which, deeply upsetting him (understandable) and prompting Cygames to say "Stop that."
What that clause really means is, "Don't tell us you're doing it." Several horse owners are indifferent regarding lewd fan art, or even welcome it. One of them specifically demanded his horse have larger breasts than another horse. Just don't tag them on gore porn on Twitter like a dickhead.