If you copy a purchased epub format book out to the Finder, you can load it into calibre, but when you try to read it, the App's embedded reader tells you:
This Book is locked by DRM. To learn more about DRM and why you cannot read or convert this book in calibre, click here.
Apple has not yet provided a method to read these books on a Mac.
Despite rumor, Thursday's education-related event produced no OSX-based iBooks reader. So the answer is still no, and will likely remain no for the forseeable future.