That's Warren Haynes on the slide not Derek Trucks. And yes they have 2 drummers, had always 2 drummers. In fact, the only original members of ABB left are the two drummers, Butch Trucks (Derek's Uncle) and Jai Johanny "Jaimoe" Johanson and Gregg Allman. They booted Dickie Betts (one of the original guitar players) just recently. Warren Haynes played with ABB for years and was regarded as the best "replacement" for who was considered one of the best slide guitar players ever, Duane Allman. Warren quit ABB to form Gov't Mule with bass player Allen Woody who played with ABB too. Allen Woody died suddenly a couple of years ago so Warren joined ABB again shortly after.
A bit of trivia, Eric Clapton learned slide from Duane Allman during their time together with the band called Derek and the Dominoes. They only did one album called "Layla and Other Assorted Love Songs" from which the song Layla came out.
Obviously I am a big ABB fan, been a fan since the first time I heard them in 1970.