you can't
You can't catch or get a Hitmontop in Emerald unless you cheat using an action replay or trade. In Pokemon FireRed and LeafGreen, choose either a Hitmonlee or Hitmonchan from the Fighting Dojo in Saffron City. Then breed the one you chose with a Ditto at Four Island's Daycare. You will get an egg that contains a Tyrogue. Raise this Tyrogue to Level 20 and make sure it has equal Attack and Defense when it evolves. This will ensure its evolution to Hitmontop. Then trade the Hitmontop to Emerald.
You can't, you have to trade from LG/FR
Yes, You can catch Groudon in Pokemon Emerald.
You can't catch one in Pokemon Emerald.
No you cannot catch Entei in Pokemon Emerald.
You can't catch a Bellsprot in Pokemon Emerald. You trade it from Pokemon Leafgreen!
There are many Pokemon you catch that are similar in sapphire and emerald but there are many Pokemon emerald can only get and not sapphire.
You can't catch or obtain other trainers Pokemon in emerald.
Cressilia is a 4th generation Pokemon so you can't catch it in Pokemon Emerald.
No you cannot catch Celebi in Pokemon Emerald.
you cant. You can only catch it in Pokemon emerald, but, you cant catch latias in emerald.
Tyrouge evolves into Hitmontop when both Attack and Defense levels are equal and it has reached a certain state of Happiness level. Other than that, Hitmontop cannot be obtained.