If you're crafty enough yes. I've played through so far and I've had a few 'rough' this person up kinda quest, but killing is prohibited by the TG.
The namby-pamby Robin-Hood-wannabes of Cyrodiil prohibited killing in Oblivion, but the mobsters of Skyrim have no such compunctions. They don't generally
require you to kill people and they try to avoid stepping on the Dark Brotherhood's toes by discouraging you from killing unnecessarily, but nobody actually cares if you do.
Unless you kill another Guild member, of course - that requires you to whine to Vex about "how will I ever come up with 1,000 gold to pay off the Guild?" even if you have a million coins burning a hole in your pocket...