No more risky than downloading something off Pirate Bay. Afrihost can't see your torrent contents if you're using encryption, but they can see volume of data moved and the IP addresses you're connecting to.
Using a VPN or proxy to bypass the uncapped Home shaping policies is against their terms, so if they do catch you doing that your account could be closed. Not sure if those terms are the same for their Business accounts, but it's an unshaped account anyway.
As mentioned elsewhere in this thread, only if you're pirating content made locally, like music, TV series like Isidingo or a movie like Tsotsi. If you're paranoid about this you can use Telkom because they don't care what you do as long as the bill is paid, although their torrent performance is incredibly sucky at this point.