I know that Pichu can't breed, but this is a Ditto. Is it different??
Pichu is a baby Pokemon, and no baby Pokemon can breed, even with Ditto.
If you want a Pichu, breed a Pikachu; it will still hatch into a Pichu.
EDIT: also, trading makes no difference in this scenario.
No, you can't breed a Pichu with Ditto or any Pokemon.