The action that will cause data loss is the formatting and re-partition that happens before you get the opportunity to reload from your Time Machine backup.
The normal process is:
- Verify last backup of any data you wish not to risk (BootCamp and Mac partitions should be backed up just in case)
- Erase the parts of the drive you wish to clear or clean
- Reinstall OS X onto the Macintosh HD part of the drive
- Start the restore process from the Recovery HD, from another bootable OS X source or from the Migration Assistant running from the newly reinstalled OS X partition
When you go to load a Time Machine (or any other backup) as long as you didn't erase the Boot Camp data partition as part of the formatting or reinstallation steps that are already complete, then you won't lose further data such as a Boot Camp partition.
The programs that load Time Machine want to write that data to the Macintosh HD side of things and leave the other partitions alone.