Is it possible/ feasible to convert ordinary nodes to Ubercart nodes? I have a site that imports content from several XML and CSV feeds, which creates nodes for each item (the items are products, but the site does not directly sell each product).

I'm just wondering if it's i) possible and ii) feasible to convert these nodes to be usable with Ubercart? Although the site doesn't directly sell the products (each product links to the supplier's site), there are features in Ubercart that are attractive to use - in particular, an Ubercart theme that I would like to use on the site.
I'm not sure how the ubercart theme you're interested in works, but you can declare any content type as an ubercart 'product' type. This would eliminate the need to convert exsiting/imported nodes, but I'm not sure if the theme you're looking at is only set up for the default Product type that ubercart creates for itself.