i know the Vipperloids have numbers on their shoulders similar to Vocaloids, i think it's because most vipps were released as "fake vocaloids" so the numbers are there to mimic vocaloids? (it's a guess)
as for what the numbers mean, i think they're just a reference to someting about the character.
Ruko's number is 65, i think i can take a safe shot that it's referring to their 6'5 height lol
Teto is 0401, probably referring to her release date of april 1st
Miko is 35, she's 3.5 yrs old
yaknow