Is there a way to tell in-game if a Pokemon can evolve other than when it is first registered?
Solution 1:
You should be able to see that screen once you have access to the Alola Pokedex, the lower screen lists every Pokemon encountered, while in the upper screen you have this view:
[Incomplete page]
[Complete page]
which is the same "screen with pokeballs in the background indicating if the Pokemon can evolve" you were talking about.
I've played only 3 hours on my Ultra Moon copy, and I already have that. But I've redeemed some gift Pokemon like shiny Solgaleo, so my Pokedex may be "biased".