Can I import VirtualBox *.ova images in KVM or I should redownload them from https://www.whonix.org/wiki/KVM#Download_Whonix ?
Always use the specific images for their respective versions.
Have a nice day,
In theory, yes. But difficult since undocumented.
Whonix KVM is more than copying over the VBox image file. The packaged XML settings are tweaked for enhanced performance and security. You lose out on that by just importing a converted image.