Hello,
Since you wanted to populate the data from your Community Builder structure, one solution is to create a custom plugin and use the trigger that I gave you.
The trigger gives a direct access to the vendor object before the creation of the entry in the database.
If you do not have development skills to create a Joomla plugin ; you can also see to use a view override for the "vendormarket / registration".
There thanks to
if( !isset($this->element->vendor_id) ) {
}
You can add some PHP code to populate the "$this->element" with data coming from your CB.
The vendor_image will be the difficult field since it contains the relative path to the image from the HikaShop upload folder.
Regards,