Nifi is basically a data ingestion tool. It can collect data from various platforms. These Data can put to HDFS and initiate processing with Hive, MapReduce, spark, etc.
Oozie is a data pipeline management and scheduler. It can group different activities like (spark, MapReduce, Hive) and process them in a single pipeline.
The main difference between both of them is 'Oozie' resources are fully managed by Yarn, whereas 'Nifi' is fully self-managed tool with pseudo-distributed mode.