Oracle Database Discussions

My coworker and I are discussing whether it is necessary, or advised, to rebuild indexes after an import of the schema.

My thinking is that the index data is put into fresh blocks thereby creating a very flat index tree without any fragmentation.
But my coworker suspects that perhaps the blocks are built exactly as they existed in the source database.

I could understand, perhaps, if the refresh were done by using RMAN which copies block by block, but even then I'm not sure.

Can you help us understand this please?

Thanks.

Ed