For example if my opponent casts noxious gearhulk and I counter with Disallow does the gear hulks ability activate or is he destroyed "before entering the battlefield" since he is not resolved? Also would the same be true for Essence ScatterThank-you.
When you counter a spell that spell is put into the GY without resolving and not of its effects occur. So if you counter Noxious Gearhulk as a spell it will simply be put into the GY and nothing happens. If you let the spell resolve and it enters the battlefield then its ETB ability will trigger. You can then counter that ability with Disallow if you like and then the trigger will be countered and do nothing.
I'm assuming you're targeting the Gearhulk spell and not its enters-the-battlefield triggered ability? The Gearhulk will never enter the battlefield if it's targeted, and therefore no ability will trigger. It is not "destroyed" since it is never on the battlefield in the first place.
Noxious Gearhulk's enters the battlefield trigger means that it has to actually resolve for the ability to trigger. It won't trigger at all if you counter the creature spell. This is as opposed to cast triggers such as World Breaker's, which have to be countered separately from the creature spell itself.
For example if my opponent casts noxious gearhulk and I counter with Disallow does the gear hulks ability activate or is he destroyed "before entering the battlefield" since he is not resolved? Also would the same be true for Essence ScatterThank-you.
When you counter a spell (the mode I assume you're using here) then the card in question doesn't get to resolve. A creature spell that is countered never enters the battlefield. If it never enters the battlefield, it's ability can never trigger. It is also not destroyed. To be destroyed, again, it has to enter the battlefield, and it won't if it was countered.
The card you mentioned is interesting because it can do more than just counter the spell. It can either counter the gearhulk outright, OR you could use it after the gearhulk resolves to counter the "Destroy another creature" ability. In this situation, there would still be a gearhulk on the battlefield, but nothing would have been destroyed.
I̟̥͍̠ͅn̩͉̣͍̬͚ͅ ̬̬͖t̯̹̞̺͖͓̯̤h̘͍̬e͙̯͈̖̼̮ ̭̬f̺̲̲̪i͙͉̟̩̰r̪̝͚͈̝̥͍̝̲s̼̻͇̘̳͔ͅt̲̺̳̗̜̪̙ ̳̺̥̻͚̗ͅm̜̜̟̰͈͓͎͇o̝̖̮̝͇m̯̻̞̼̫̗͓̤e̩̯̬̮̩n͎̱̪̲̹͖t͇̖s̰̮ͅ,̤̲͙̻̭̻̯̹̰ ̖t̫̙̺̯͖͚̯ͅh͙̯̦̳̗̰̟e͖̪͉̼̯ ̪͕g̞̣͔a̗̦t̬̬͓͙̫̖̭̻e̩̻̯ ̜̖̦̖̤̭͙̬t̞̹̥̪͎͉ͅo͕͚͍͇̲͇͓̺ ̭̬͙͈̣̻t͈͍͙͓̫̖͙̩h̪̬̖̙e̗͈ ̗̬̟̞̺̤͉̯ͅa̦̯͚̙̜̮f͉͙̲̣̞̼t̪̤̞̣͚e̲͉̳̥r͇̪̙͚͓l̥̞̞͎̹̯̹ͅi͓̬f̮̥̬̞͈ͅe͎ ̟̩̤̳̠̯̩̯o̮̘̲p̟͚̣̞͉͓e͍̩̣n͔̼͕͚̜e̬̱d̼̘͎̖̹͍̮̠,͖̺̭̱̮ ̣̲͖̬̪̭̥a̪͚n̟̲̝̤̤̞̗d̘̱̗͇̮͕̳͕͔ ͖̞͉͎t̹̙͎h̰̱͉̗e̪̞̱̝̹̩ͅ ̠̱̩̭̦p̯̙e͓o̳͚̰̯̺̱̰͔̘p̬͎̱̣̼̩͇l̗̟̖͚̠e̱͉͔̱̦̬̟̙ ̖͚̪͔̼̦w̺̖̤̱e͖̗̻̦͓̖̘̜r̭̥e͔̹̫̱͕̦̰͕ ̗͔̠p̠̗͍͍̱̳̠r̰͔͎̰o͉̥͓̰͚̥s̟͚̹̱͔̣t͉̙̳̖͖̪̮r̥̘̥͙̹a͉̟̫̟̳̠̟̭t͈̜̰͈͎e̞̣̭̲̬ ͚̗̯̟͙i͍͖̰̘̦͖͉ṇ̮̻̯̦̲̩͍ ̦̮͚̫̤t͉͖̫͕ͅͅh͙̮̻̘̣̮̼e͕̺ ͙l͕̠͎̰̥i̲͓͉̲g̫̳̟͈͇̖h̠̦̖t͓̯͎̗ ̳̪̘̟̙̩̦o̫̲f̙͔̰̙̠ ̹̪̗͇̯t͖̼̼͉͖̬h̹͇̩e͚̖̺̤͉̹͕̪ ͚͓̭̝̺G͎̗̯̩o̫̯̮̟̮̳̘d̜̲͙̠-̩̳̯̲̗̜P̹̘̥͉̝h͍͈̗̖̝ͅa͍̗̮̼̗r̜̖͇̙̺a̭̺͔̞̳͈o̪̣͓̯̬͙̯̰̗h̖̦͈̥̯͔.͇̣̙̝
When you counter a spell (the mode I assume you're using here) then the card in question doesn't get to resolve. A creature spell that is countered never enters the battlefield. If it never enters the battlefield, it's ability can never trigger. It is also not destroyed. To be destroyed, again, it has to enter the battlefield, and it won't if it was countered.
The card you mentioned is interesting because it can do more than just counter the spell. It can either counter the gearhulk outright, OR you could use it after the gearhulk resolves to counter the "Destroy another creature" ability. In this situation, there would still be a gearhulk on the battlefield, but nothing would have been destroyed.