As for remakes, no, no new Pokemon were introduced into a generation when a game was remade, however, alternate forms, for example, Mega Swampert in ORAS and Sky Shaymin and Origin Giratina in Platinum, have been introduced in remakes. As for sequels and other games that didn't start the generation, yes, there have been a few Pokemon. To my knowledge, they are Poiple, Naganadel, Blacephalon, Stakataka, Zeraora, (all in USUM) Meltan, and Melmetal (in LGPE)
EDIT: There's also Black and White Kyurem in B2/W2 and Dusk Mane, Dawn Wings, and Ultra Necrozma in US/UM.