I work with a few former-Oracle DBAs in a PostgreSQL-flavored consultancy now and they are aces. All the root-cause analysis and organization skills transfer handily.
Postgres is functionally and conceptually extremely similar to Oracle. There are a few oddities (in particular, oracle's "nulls are never in indexes" is kinda weird) but the redo log is similar to the WAL, etc. In most cases, similar approaches will perform similarly and experience pretty much transfers over with a few months of experience.
