Could I Beat The Elite4 On Pokemon Platinum?

It depends on what pokemon you have.  If you have beaten all the gym leaders and gone into the reverse world, your pokemon should have the ability to defeat them.

Recommendations and facts that may help:
AARON
Pokemon: 1. Yanmega, 2. Drapion, 3.  Heracross, 4. Vespiquen, 5.Scizor.
Type(s): Bug
Recommended types: YANMEGA=Fire, Flying, Electric, Rock, Ice.
BERTHA
Pokemon: 1. Whiscash, 2. Gliscor, 3. Golem, 4. Rhyperior, 5. Hippowdon
Type(s): Ground
Recommended types: Grass, Ice, Water, Steel
FLINT
Pokemon: 1. Rapidash, 2. Houndoom, 3. Flareon, 4. Magmortar, 5. Infernape
Type(s):Fire
Recommended types: Water, Ground,Rock.
LUCIAN
Pokemon: 1. Mr. Mime, 2. Espeon, 3. Bronzong, 4. Alakazam, 5. Gallade
Type(s):Psychic
Recommended types: Ghost, Bug, Dark, Fire, Flying
CYNTHIA
Pokemon: 1. Spiritomb, 2. Togekiss, 3. Lucario, 4. Garchomp, 5. Roserade, 6. Milotic
Types: 1. Ghost/Dark, 2. Normal/Flying, 3. Fighting/Steel, 4.  Dragon/Ground, 5. Grass/Poison, 6. Water
Recommended types: 1. Any strong pokemon, 2. Electric, Ice, Rock, 3. Fire, Fighting, Ground, 4. Ice, Dragon, 5. Fire, Ice, Flying, Psychic, 6. Grass, Electric

Now go out there and show those losers who is boss!