yo could but why would you need to unless you evolving certain Pokemon like Kadabra to Allakazam or gravalar to golem or clamperlto Huntail or Gorebyss depending on if its holding a deep sea tooth or a deep sea scale
no need to trade. the word you are looking for is "migrate".if your thinking of trading,i`m sorry but you cant.but to migrate,read the Pokemon pearl instruction booklet.
You can trade with another sapphire, ruby, emerald, firered, leafgreen, Pokemon colosseum, Pokemon xd gale of darkness and Pokemon box ruby and sapphire.
Yes. Obtain the National Pokedex. Load Pokemon Sapphire into the slot 2 in the DS. Start Pokemon Diamond. On the main menu, select "Migrate from Pokemon Sapphire". Follow the on-screen instructions.