I don’t think this is set in the reboot universe, this looks to be a somewhat shot to shot remake of the first movie but in CG. Even the original writer, who’s no longer with us, is credited for writing it.
I did wonder if that were the case, maybe they’ll just reuse the voice track and music from the original, but Mewtwo’s VA seems to have confirmed they’re recording a new voice track. Gotta be interesting to see what the Dub will do, will they leave in the music like the Power of Us letting Western fans finally hear the original Japanese music core (if its not a new one.), reuse the original’s English dub’s score (Though likely without the pop songs) or record an all new score together that either recreates tunes from the original’s dub or new music entirely much like movie’s 17-20? Course, it’ll probably be the TPCI’s current VAs as Ash and co….maybe.