You seem like a good person to ask this question to, but I don't know if this is a question you can answer. Are Vocaloid OCs 'ok'?
hmmm to tell you the truth i’m not sure! i’ve never really seen a vocaloid OC before, besides derivatives or MMD recolors.
what I do know is that…. if the character is sorta derived and based on an original vocaloid, its fairly alright, as long as its not a complete recolor. for example, note the small differences between Hatsune Miku and her derivative Zatsune Miku. Zatsune may seem like a recolor of Hatsune, but there are small differences in her clothing.
A few more examples of derivative characters include Akita Neru, and Haku Yowane, who are both based on Hatsune Miku, and in some way also represent her (Haku and Akita both represent poor use of Hatsune Miku.)
There are also more unique, non-vocaloid, but still closely related characters such as Calne Ca, Calcium, Black Rock Shooter, Ene.
“OC” characters that are something like those is generally okay. basically, if you create, lets call it, another version of an existing vocaloid, then its totally fine! and also very interesting. its fun to create new completely original personalities for characters that already exist.
anyways, as for an actual completely original vocaloid character that doesnt really exist…. i really don’t know about that. i’ve never exactly seen one tbh. the only things i can think of are the characters that are just based on pre-existing vocaloids.
hm… i guess i’d say if you really wanna try to create your own original unique vocaloid-type character, make an UTAU instead! UTAU is extremely similar to vocaloid, except its totally free. and you can use your very own voice to make one that can sing too! as far as UTAUs go, creating original characters that are very similar vocaloid is totally okay. if anything, you can actually think of it as being able to create your very own vocaloid, with a voice and all! please look into that if you’re interested. ^ ^