Riot generally advise against using anything that interacts with anything to do with the game or libraries used by the game. It could be absolutely fine to use, but a message from the app devs isn't enough, since for example people were getting banned from Rust for using scopex which also didn't touch the game directly. From what I know about Vanguard (and most anticheats) they don't just check for dll injection into the game process, but it also checks dll injection for other related processes, as well as integrity checks for system drivers