You cannot catch Deoxys in the wild on Pearl or Diamond. You must migrate it from one of the past versions that you caught it on. For example, you can catch it on Emerald and migrate it to Diamond.
You would need to use an Action Replay or transfer it from Pokemon Emerald, FireRed, or LeafGreen, for it is impossible to catch Deoxys in any location in Pokemon Diamond, Pearl, and Platinum.
No you can't catch deoxys by using cheats
neither of them is better, they are both the same, but in diamond, you catch dialga, and in pearl, you catch palkia, and you can catch different Pokemon in each game for example: you can catch this Pokemon in diamond, but not pearl but: you can catch this different Pokemon in pearl, but not diamond
yes if you have cheats
you cant, get a action replay
trade diamond from Pokemon diamond onto Pokemon pearl
Not much. Pokemon diamond and Pokemon pearl have different Pokemon. for example, in pearl you can catch a glameow but not a cranidos and in diamond you can catch a cranidos but not a gleameow. And at the end of pearl you can catch Palkia the legendary and at the end of Diamond you can catch Diagla. But the games are basically the same. And there you go.....
In a way. In pearl, you catch palkia. And in diamond, you catch dialga.
You cannot catch Palkia on Pokemon Diamond and you cannot catch Dialga on Pokemon Pearl.
You cannot catch Raikou in Pokemon Diamond and Pearl. To get Raikou in Pokemon Diamond and Pearl, you must trade for one from Pokemon HeartGold and SoulSilver where it can be caught or transferring from Pokemon FireRed and LeafGreen.