Meloetta cannot be shiny. That is the default status of any Wonder Card Pokemon; except for Strongest Pikachu and the Japanese Kyushu Pokemon.
And about that thing with Gift Pokemon not advancing the PID frame: It is correct, but there are a few general exceptions when there is a trait contrary to the PID is forced, like Dratini/Gible (shiny), the black Haxorus (shiny) and that Eevee from Amanita (gender). In that case the PID frame is advanced by 1 before the Pokemon is actually generated.
And about that thing with Gift Pokemon not advancing the PID frame: It is correct, but there are a few general exceptions when there is a trait contrary to the PID is forced, like Dratini/Gible (shiny), the black Haxorus (shiny) and that Eevee from Amanita (gender). In that case the PID frame is advanced by 1 before the Pokemon is actually generated.