The encryption in Hamachi can be disabled per client. You can have a mixture of encrypted and unencrypted peers in any given Network.

Open the client and go to System > Preferences > Advanced Settings. Under Peer Connections > Encryption select an option :

1. Enabled: Default. This client can talk to any other client that has encryption enabled.
2. Disabled: This client can talk to any other client that has encryption disabled.
3. Any: This client can talk to any other client regardless of whether encryption is on or off.