If you successfully capture a poisoned Digimon, it keeps the poisoned status when it joins your party, so it can still take poison damage at the end of the turn. That part is intentional!
And yes, there are more shiny Digimon! Some Digimon don’t have shiny colors added yet, but if you catch one as shiny now, it will still become its shiny-colored version later once its shiny palette is added in a future patch.
Also, Keramon’s sprite is already finished, and I’m currently adding content related to its quest line!