SQL Indexed View for Datamart Reporting with Transactional Replication
Yes.  It is generally safe, and often useful to create indexed views on subscriber tables in transactional replication.

You may need to drop and recreate the indexed views using custom scripts before and after initializing from a snapshot.  See Execute Scripts Before and After the Snapshot Is Applied 

You can also use a different indexing scheme on the subscriber (also by using post-snapshot scripts). In particular you can make the subscriber tables Clustered Columnstore tables, or add non-clustered Columnstore indexes on them for reporting.