Volume Shadow Copy based backup that works with TrueCrypt?

While the TrueCrypt disk drive is mounted and is formatted with a file system, you should be able to use any disk-to-file backup product or disk-to-zip. There are many such products that use Volume Shadow Copy and can copy all files on the disk, some of which are:

FBackup
Cobian Backup
GFI Backup 2009 Home Edition

However, the best and the most complete is AOMEI Backupper, which can favorably compare with any other commercial product on the market.

Unfortunately this is not possible. The Truecrypt website lists Volume Shadow Copy as a current limitation.

The Windows Volume Shadow Copy Service is currently supported only for partitions within the key scope of system encryption (for example, a system partition encrypted by TrueCrypt or a non-system partition located on a system drive encrypted by TrueCrypt). Note: For other types of volumes, the Volume Shadow Copy Service is not supported because the documentation for the necessary API is available from Microsoft only under a non-disclosure agreement (which is impossible to comply with because TrueCrypt is open source).

I’ve found a very simple solution with windows' embed backup system! There is a posibility to backup to the network shared folder. You just have to make a folder on encrypted drive and share it. Then you can click “Save on a network…” button at Set up backup dialog and choose your own computer and your shared folder on encrypted disk.

The “Save on a network…” solution works! You just have to use "Properties" -> "Advanced Sharing" and share it with the System group. Then you can select the \localhost\folder path in Windows backup.