The Doobie Brothers were a classic rock staple with smooth, catchy songs that boogied—and country music circa 2014 has more in common with classic rock than with the country music of the ‘50s and ’60s. So, it’s an easy transition for The Doobie Brothers to invite a variety of country singers to join their vocalists on the hits. Sure enough, Blake Shelton and Tom Johnston tee off on “Listen to the Music.” Sara Evans takes on “What a Fool Believes” with Michael McDonald in fine form, and Patrick Simmons and The Zac Brown Band work on “Black Water” as if the songs had been written with them in mind.