Some Macne based/inspired UTAU such as Makune Hachi and Makne Nitton as example actually looks good but they look still original and not look a "rip-off" or "re-color" of official Macne.
I am OK if people creates a character (fan character) based on Crypton/Macne (or any other game/cartoon series in general e.g. MLP, Sonic etc) as long as they look someway original but also details that are added in somehow are in harmony with original series and the fan character looks like that it could be an official character of that show/series and so on.
But let's be honest: creating a GOOD fan character/design is extra hard and can limítate creator's imagination because you need to often use specific (drawing) style, colors, detales and/or body types etc to "match in", so it becomes very easily "repetitive".
I think that if you like Crypton/Macne based design then OK, you can create one (as long as not a recolor of course) but keep in mind that this theme has become really overused over the years (from 2008/2009!!) so standing out from a crowd now in 2017 is much much more difficult. If you want that your UTAU stands out better from a crowd, I recommend to base it on something own, original, thing.