Masters is a spin-off, not a main series game. PokeSpe only adapts main series games, not spin-offs. You can even see that in the fact that it has never adapted Colosseum and XD, which were the spin-offs that were the most similar to the main series. Technically, Kusaka's Ranger manga are set in the same universe as PokeSpe, and the first one was even directly referenced in the Platinum arc for Manaphy's backstory, but they are not published in PokeSpe volumes.
That said, I do think we could see Red wearing his Masters clothes, and maybe some Sygna Suits appearing in PokeSpe if we ever see previous characters again. Maybe we might even see Professor Hinagiku if she is referenced or appears in main series games. Heck, maybe we could even get cameos from the protagonists and rival. But we will NOT get a Masters arc.