Totally viable, focus on venoms and liberally use dancing dagger and you essentially just have a permanent 10% damage boost across the board. Then you're right there with me with an identical critical strikes line. God bless the executioner.
You've also shown great class by investing the points necessary for Preparedness
Re: shadow arts vs. either Deadly/Critical for roaming- just depends what you're looking for. Shadow Arts will make you imminently more survivable, the other two will significantly increase DPS. Shadow Arts really excels at the "turning a vulnerable position into an advantage" game. Low on health, when you use Hide in Shadows suddenly you gain initiative and do extra damage coming out of stealth.
One thing I'd say is that silly as it sounds, investing 10 points into acrobatics is well worth it to me for swiftness on dodge and the major trait, which gives you the ability to swap between a number of situationally-useful abilities including the fall damage trait (lifesaver in some areas). Course, this comes at the expense of overall "doing something" effectiveness.
What weapons do you run?