We can now be certain the Ultra-Beasts are able to be captured: they are included in the national Alola pokedex, which you can find
here (obviously huge spoilers). I am... disappointed to be honest. I expected more from Alola. Poor Komala does not get an evolution. I am not a fan of Pikipek's evolution. Counting all new pokemon in addition to ultra beasts, you will get a 62. Counting Alola forms as new, you will get +18, if I am not mistaken.
No new mega-evolutions which SUCKS so hard, I cannot even describe it honestly. I really do not understand why they didn't expand on mega-evolution this generation. I am really hoping that these leaks are not final, and there's still room for discovery, but I highly doubt the way it looks.
Also, as a note to those that have been wondering all this time: The starter leaks are real, and there does not seem to be any secret behind the starters for now. I really like all the starter evolutions to be honest. I will want them all on release! Anyone that wants to help me do that when the games release? It would be greatly appreciated :-)