A few paragraphs in the documentation suggest that the WAL is created locally and only copied to HDFS for/during recovery.
The Master will coordinate the copying of write-ahead logs to HDFS so the logs are available to all tablet servers.
Recovery is performed by asking the loggers to copy their write-ahead logs into HDFS. As the logs are copied, they are also sorted, so that tablets can easily find their missing updates. The copy/sort status of each file is displayed on Accumulo monitor status page.