Is it possible to get Poni Grove Pokemon before the postgame?

Question

is there some sort of exploit to get past the man who stops you from going to Poni Grove before beating the Elite Four in Ultra Sun?

Answer 1

Unfortunately, there's no way to access the Poni Grove until you become the Champion. You can still obtain its Pokemon earlier through trading. Pinsir, Buneary, Zoroark, and Trumbeak are also available in other locations.

Bulbapedia's list of glitches in Generation VII doesn't mention any type of useful exploit, so it's safe to say there's no glitches to get into Poni Grove either.