When country artists are looking for the kind of slamming, funky beat that opens Thomas Rhett’s “T-Shirt,” they get the right man for the job: Chris Kimmerer, a Canadian drum demon who’s become a Nashville session monster. Kimmerer didn’t get where he is by being a one-trick pony. He’s just as dialed in when he brings a slow-rolling, understated groove to a slinky ballad like Kelsea Ballerini’s R&B-inflected “a country song.”