Restoring the database dump of a newer version to an older version of mongodb
Assuming you aren't using any newer features or index/collection options from MongoDB 3.2+ that aren't supported in MongoDB 3.0, you should be able to restore the backup.

Before doing so, I would review the downgrade instructions in the MongoDB documentation to check for potential issues:


Downgrade MongoDB 3.4 to 3.2
Downgrade MongoDB from 3.2


The downgrade instructions assume a change of binaries rather than a mongodump backup, but the caveats on backward-incompatible features such as newer index and collection options still apply.

I suggest using the 3.4 versions of mongodump and mongorestore  to test your outcome in a development or staging environment before applying to a production deployment.