Tetsuya Endo えんどうてつや
Director of the PlayStation game's animated segments (resolves the earlier '?')
Konaka's 2018 blog makes Endo's role clear: Konaka wrote the scenarios for about thirty minutes of animated parts in the PlayStation game, and Endo was the director who turned them into film. This fits Japanese Wikipedia listing him as the game's 監督 alongside Junji Nakahara as director. Endo's own filmography also credits him on lain BOOTLEG (1999). He is an anime director and sound director known for music-centered series. Konaka describes his own part in the game as little more than a go-between from Ueda's plot to Endo's film, so Endo should be credited for how those game movies look. The game's own staff list settles the split: it credits Junji Nakahara as Director and Endo as Director & Storyboard of the MOVIE part, so Endo did not direct the whole game.
Sources: ja.wikipedia.org archived · ja.wikipedia.org archived · yamaki-nyx.hatenablog.com · animenewsnetwork.com