I have a client who wants me to set up a website for him with a eCommerce back-end on it. He's not going to be doing anything too commercially heavy, so I figured I would go with Joomla and VirtueMart. Being a new fan of RT I figured it would be great to have him pay for a subscription and just have me build a RT theme around his VirtueMart install.
My question therein lies, since I've never setup VirtueMart before... do I need a VM-specific theme or can I indeed wrap a RT theme around it without too much additional coding?
You don't need to wrap it. VirtueMart is a Joomla component. It uses your Joomla template. You might want to customize the icons to match your Joomla template.