From your source, it uses the same key:
> Write Ahead Log Files - Using the new WAL mode (i.e. PRAGMA journal_mode = WAL;), page data stored in the WAL file is encrypted using the datbase key. Pages in the rollback journal are encrypted using the same key as the main database. Verification: create an encrypted database, start a transaction, make changes, and then inspect the -wal file using hexdump or a similar program.