Yes, you can! Any disk drive that your operating system (Windows, MacOS, or Linux) recognizes as an attached (mounted) drive can be selected from within the Hiver desktop application.
However, this is not a recommended setup because of the high probability of having an outage due to overheating of the external connector or controller. It would be better to use an internal drive.
A network connected drive could also work under some special circumstances, but this configuration is likewise not supported nor recommended.