Nietzsche sees Christianity itself as a sort of mob action to suppress excellence and freedom, and he sees the way it acts as entirely based on nonexistent virtues that are actually self-deceptions.
The virtue of humility is not despicable because of what it is, it is despicable because it really is never what it claims to be. It is really a move in a competition to be a 'better person' than others, to more thoroughly support the common good over one's individual good because his sense of his own value is reflected in common social interests, rather than in natural ones.
Someone with an honest awareness of his value, even if that value is low, is not humble, he is honest, and adapts to reality. He does not consider his humility a virtue.
Someone like Gandhi, who adopts a lowly lifestyle out of compassion for others, and uses it to manipulate those with an equally false worldview into admitting they are lying to themselves, is not humble, he is fair, brave, and shrewd. Those are virtues, but those virtues are not humility.
The obvious fraud is given away by the fact that this 'common good' is only so common. This ideology of loving others instead makes its supposed adherents the ones most likely to go to war with them, to create ways to indirectly dominate them, or to force them into a mold of the dominant culture's choosing.
No one is actually humble. So whether there could be non-despicable humility of some sort doesn't matter.