They can definitely have print version added. The price for added print cover (back cover and spine) is $50 on RockingBookCovers.com. I need page count, page size and back cover blurb information in order to make it. Print versions can also be bought later, not at the same time as ebook covers.
In general, most designers make the ebook cover/front cover first and put it up for sale. Then if author needs and orders the print cover, the designer will make it with no issue and match it to the front/ebook cover. Often, authors release the ebook version first, test the waters, and then decide if they should add the print version. They can always order a print version later on.
Usually the designer charges some fee for print version. But there are some designers who make the cover with print version too, at once. The price often reflects that too (covers with print are more expensive).