The kinship between Orphic and Pythagorean ideas is confirmed by a number of sources, so your note about Pythagorean butterflies is helpful. The best article I've seen on this, as related to Nabokov, is David Larmour's essay in Metamorphoses in Russian Modernism. See here:
Phanes, insomuch as he is winged, may himself resemble a butterfly--thus the conjecture regarding the genus name. I wonder, however, how Kinbote, who knew very little about butterflies, would have known this altogether obsolete entomological variation on Vanessa. Doesn't this require a deeper knowledge than we're used to seeing in Kinbote?
I am still trying to understand your connection to evanescence. Phane as a suffix means to appear, and phanero- as a prefix means visible, manifest, so evanescence is its antonym; but how does that relate to Nabokov? As for the skin, phaneromania is defined by Webster's 2nd as "a morbid habit of picking at some abnormal growth on the skin, biting the nails, or the like." They may put us in mind of Hazel, who sits on her bed "scratching her head with psoriatic fingernails."