I think no, but you can trade or battle in wi-fi. battling i hard, so it's probly better by trading over the gts, and you can trade one.
No
There is no Lumineon in diamond
yes
The Sinnoh League Champion "Cynthia" has a Spiritomb.
use a master ball if you haven't got any u cant
Im not sure but u can catch krabby during swarm.
None of the 4th gen Pokemon exist in any of the 1-3 gen Pokemon games meaning nothing like electivire exists in firered or any game before that.
If you really want to, use your masterball because it never fails. Masterball fails on other peoples Pokemon. I learnt from my mistakes... you cant catch trainers Pokemon it wont work with any type of poke ball(it would've been cool if you can catch trainers Pokemon though=)
No, unless you have a National Pokedex you might find a trainer who has one in the Battle Tower.
you can get any Pokemon there when you have beaten darkrai: electivire charizard gliscor etc
Electivire is a 4th generation Pokemon meaning it was created after the GBA Pokemon games so that means its not obtainable in any GBA game including emerald.
An Ace Trainer in Victory Road on floor B1F has one. Sorry, scratch that, the Metang only appears in Pokemon Platinum.