Software Raid 10 on VirtualBox?

Yes, this will work. Of course, don't expect to get any performance gain as the underlying disks are on the same device, but it's a great way to learn how to set it up in a safe environment.

As Kyle said, this will work. The setup and administration tasks will be identical to a physical system. As additional benefit, You can simulate the removal and replacement of a disk without fiddling with five disks.

However:

• There won't be any redundancy. Therefore, Your raid is as vulnerable as the host file system.
• I/O performance will be very low. Every write access results in two physical writes on two different parts of the same physical disc on the host system.