I personally do not believe UB2-Absobtion is Gladion because he owns Type: Null. Type: Null and it's evolution was created to oppose a threat. Though not directly stated, I believe this threat are Ultra Beasts. Gladion is not an Ultra Beast, he wants to purge the world of Ultra Beasts.

My guess to who UB2-Absorbtion really is is Faba. Faba's glasses make his eyes look bug like, which is what UB2 looks like. He also has a distinctly pointy nose, which could become UB2's long sharp nose. His scrawny human appearance could be a cover up for his true strength.