7 speed shimano sti shifters work 100% perfect on the SRAM 3x7 Dualdrive (ffront and rear). However, it might be a trick to find 7spd sti shifters. ALso, I don't know if they'll work on the 3x9. Since the hub gears on the 3x7's and 3x9's shift in the opposite direction (I know, I have both) I have a slight concern that the cable pull may also be different. (SRAM is also pretty unafraid to mix things up with non-standard cable pull ala their x-0 rear derailleurs.)
I'd say the chances are high it will work fine, but there's good reason to wonder.