I'd say no on the rotodex stuff, since that was just implemented in the games to make them less challenging.  As for Necrozma, again no.  It gets it's power from Light, not Aura, so your Aura abilities wouldn't affect it.  No, you'd need to combine it with Solgaleo or Lunala to give it that extra bit of light, then the power from the Z-Power ring, just like the games.

Also, I'd like to claim Poipole, Cosmog, Tapu Lele, and Zeraora.  Also, as of USUM, all other Ultra Beasts basically have infinite numbers, so they're not really considered Legendary, especially since their base stat total is lower than the psudoes.