Short answer: Yes. Minor characters are permitted in adult projects as long as they are not depicted nude or involved in sexual situations in any way. The content restriction applies specifically to the combination of a minor character and sexual or nude content - a clothed, non-sexual minor side character (such as a background figure, family member, or narrative presence) does not violate this rule.
What is and isn't allowed
Minor characters may appear in adult projects when they are fully clothed and play no role in sexual scenes or situations. The rule that triggers a violation is the pairing of a minor character with nudity or sexual content - neither element alone (a minor character, or adult sexual content elsewhere in the project) creates a problem on its own. There is no restriction on minor characters simply existing within the story.
Edge cases to keep in mind
Even incidental depictions follow the same line: if a minor character appears in the same scene as sexual content - even passively, even in the background - that is likely to fall into prohibited territory. Keep sexual scenes strictly to adult characters. If you are uncertain whether a character reads as a minor, consider making their adult age explicit in the narrative or character metadata to avoid ambiguity during review.
How this applies across Vizno and Vizno Uncut
This rule applies equally to projects published on Vizno and on Vizno Uncut. Vizno Uncut unlocks explicit adult content for eligible creators, but it does not relax any rules regarding minors. The permitted/prohibited boundary - minor characters are fine; minor characters in sexual or nude contexts are never permitted - is the same on both fronts.