No, there is only 1 Heatran in Pokémon Diamond.
aggron is weaker than heatran by a mile simply because heatran is a legendary Pokemon
No you can not have more than one login in Pokemon diamond.
I believe that Pokemon platinum is better than diamond and pearl because it offers more features, and allows you to do much more cheats and tricks and get more Pokemon through normal game play than Pokemon diamond and pearl. Yes, it is.
no no
the other ones go to the PC
It is impossible to find it more than once, but if you have Action Replay or a R4 card you can get it as many times as you want.
Trade it off the GTS or catch it in Pearl, Diamond or Platinum and get a friend to help you trade it over. Or you can get the Heatran from Pokemon Ranger: Guardian Signs. Other than that, Heatran isn't in the game. (Heatran comes both Male or Female, but they cannot breed. Only one Legendary breeds and that is Manaphy, so you can get Phione. Just like Cresselia is only female, and Latias and Latios.)
No! It's only 1 way sorry...
no
well... U CANT :)
yes
I wish.