Adler is the member most interested in a GN'R reunion, probably because he needs money, not being nearly as successful as the other ex-members. He hasn't had time to be successful really, as the poor guy never kicked his drug habit. He's been in and out of rehab ever since he was fired from Guns. This hasn't given him time to achieve much in comparison to the others.
He has a band called Adler's Appetite, who mainly perform old GN'R songs and other covers of bands like Thin Lizzy, Led Zeppelin and Aerosmith. They have released several original songs on EPs though. Slash, Duff and Izzy have all guested with them on stage at some point. They've also done a few tours, but nothing recently.
Adler has been in and out of rehab and has done/ is doing (not sure) a second stint with Dr. Drew on Celebrity Rehab.
And yes, he played on Slash's solo album on 'Baby Can't Drive'.
He's also released an autobiography last year: 'My Appetite For Destruction: Sex, Drugs and Guns N' Roses'
Love GN'R and follow all the ex-members to some extent.