Are the files on the mirror viewable using Windows Explorer just like the source files?
When files are deleted from the source are they deleted form the mirror?
Here are the answers to your questions:
1. Yes, if you use the Mirror backup type, the files in destination are an exact copy of the sources files. You can view them as the source files using Windows Explorer.
2. The files in backup are deleted only if you use the "Remove excluded or deleted files from backup" option from Backup Properties->Mirror page.