Your description of the problem lacks detail. Is it the the browser that has been virtualized? If so, what version of the browser are we talking about (assuming we're talking about IE)? If it isn't the browser, is it a virtual app that calls the browser? If it's the latter, your browser should function normally. If you're using a virtualized browser, your excel addin would have to be present when you use the ThinApp Snapshot to create the app.
The level of isolation will also affect the behaviour of your app.
In any event, I have cereated a virtual browser that can launch office apps when it logs in to a web app that is used to view/edit records on a CRM database system, so that is possible.