Hello,
The domain registration module in WHMCS is a native module integrated by them with Resellerclub. We will not be able to comment on the transfer options available in the WHMCS panel as it's a 3rd party tool.
However, if you are looking at Transferring Domain Names to ResellerClub, you can use the Bulk Transfer option in the Control Panel. To be able to do so, please follow the path- Product > Bulk Tools > Bulk Transfer
For more information on Bulk Transfers, you can go through http://manage.resellerclub.com/kb/answer/2474
For better assistance, you can also get in touch with the Support Team and they will guide you step-by-step through the entire process.