Looks like it. A rex usually has smoother leaves and they often grow from a rhizome just like those known as rhizomatous. Rhizos usually have bumpy or warty leaves and they are often referred to as Rex's.
There are so many new hybrids out there the term is used widely for any fancy leaved begonia no matter what they technically are.
Check out the categories and some of the photos, there are a lot of similarities.
http://www.begonias.org/greenh...