The names and relations between Violet Knox and Ronald Oranger have always intrigued me. I was able to google up Brian Boyd's surmise that there might be a link between John Rae, Jr and Oranger. There certainly is a consonance there, as probably intended by VN. But I don't think it solves what I perceive to be a riddle.
I may have stumbled on at least part of the solution. I think VN is referring to Monsignor Ronald Knox. From the Wikipedia article I noticed his associations with Sherlock Holmes & G K Chesterton that could link him to interests of VN. But they aren't sufficient to explain his "appearance" in Ada, if that it be. Therefore, I suspect it's the monsignor's famous limerick that holds the key.
Monsignor Ronald Knox
Here is the limerick which was Knox's humorous comment on the pre-existential philosopher Berkeley's concerns about perceptions and reality:
There was a young man who said "God
Must think it exceedingly odd
If he finds that this tree
Continues to be
When there's no one
About in the quad."
"Dear Sir, your astontishment's odd,
I am always about in the quad;
And thefore the tree
Will continue to be
Since observed by
Yours faithfully, God."
My guess is that Oranger is an anglicism of "orangier" (orange tree) and refers to Berkeley's Dialogues between Hylas and Philonous:
Philonous: Ask the gardner why he thinks yonder cherry tree exists in the garden, and he shall tell you, because he sees and feels it; in a word, because he perceives it by his senses. Ask him, why he thinks an orange tree not to be there, and he shall tell you, because he does not perceive it.
unSeen Kunin
p.s. By the way, this is not the first time that VN refers to a famous limerick; recall his reference to the Cabot Lodge limerick in PF which coincidently deals with conversations between man and the Almighty (Here's to good old Boston/the land of the Bean and the Cod/ Where the Cabots speak only to Lodges/ and the Lodges speak only to God)
p.p.s. None of which explains Violet (not inviolate?).