You would thinks so. But I had bought a Samsung TB T5 Portable Solid-State Drive, which could not be used. Luckily B&H accepted the return. Here is the full response I had gotten from Backblaze:
Thank you for contacting Backblaze support.
Backblaze does not support the inclusion of removable media in Backblaze backups, including CD's, DVD'd, SD cards, zip disks, floppy disks, and other similar storage devices. [Bolding theirs]
To backup this data it would need to be moved to an internal drive, or a drive connected via USB, Firewire, or Thunderbolt. While it would not be possible to give you an exhaustive list of the compatible drives, as long as the drive is not considered a temporary storage device as described above, it should be fine.
Flash keys may or may not be able to backup depending on its designation. If it is designated by your operating system as temporary storage which cannot be changed. If this is the case Backblaze will be unable to backup this drive, and you will need to copy these files to another backed up drive to backup the files.

