Thank you for your post into the forum.
The simple answer to your question is yes, you can take an encrypted backup using SQL Backup 6 of a database using compressed files created using SQL Storage Compress.
SQL Backup relies upon SQL Server to collect the backup data. SQL Server is totally unaware that the database files are compressed. So when data is read from the database files, the data is uncompressed before being passed to SQL Server.
SQL Storage Compress uses the HyperBac Technology to compress and uncompress data to and from the database files. When SQL Server reads from the database to collect the backup data, the read process is intercepted by the HyperBac Technology, the required backup data held in the compressed database files is uncompressed and passed to SQL Server.
Once SQL Server has collected the backup data, via the Virtual Device Interface (VDI), SQL Server informs SQL Backup where to find the backup data. SQL Backup will then compress and encrypt the data before writing the backup data to disk.
I hope the above answers your question.