Yes. Weakening Blast increases the bonus damage / consumes weakness stacks when Cull is used.
Prepping TA then burning Weakening Blast / Corrosive 'Nade + Dart / Frag if outside of range / Shiv if in range / Cull / Cull is great. Don't listen to everyone that rants and raves about Concealment Operatives being the only viable PVP/PVE DPS. Try them both out and make the decision for yourself.
For me personally? I prefer Lethality Tree for two reasons. Sort of.
1) AOEs + DOTs + AOE-DOT. Speaks for itself. You can spread damage out across multiple targets and can still do damage while focused/fleeing/CC'd.
2) More ways to open on an opponent. The thing Concealment Operatives forget is, there are few ways for you to enter your combo. Since Concealment Op's do the majority (not all) of their damage in Melee, you must close the gap on your target, which may or may not flee you if visible (see: Kiting). While Sever Tendon is a great starter to shutdown a target and get in close for your Melee, Sever Tendon breaks stealth, opting you out from using Hidden Strike, one of your largest sources of melee damage. While you could, in theory, Server Tendon / Cloaking Screen / Hidden Strike / Debilitate / Shiv / etc., it burns your escape and, you're reliant on the long CD of Cloaking Screen. In contrast, Lethality Ops do most of their damage regardless of stealth (though Hidden Strike is always welcome burst) and has a slow built right into their AOE-DOT, Corrosive Grenade, which aids in closing gaps. This leaves Stealth and Cloaking Screen not so much as an opener but rather, an escape mechanism, a scouting tool, and so on.
However, Lethality Ops burn Energy Fast. Even with Adrenaline Probe + Stim Boost (mind you, Stim Boost burns TA, preventing you from Culling) you can often "bottom out" on Energy, leaving you with a dreaded few seconds of auto-attacking, until you can begin the dance once again. In contrast, Concealment Ops are fairly light on the consumption of Energy and, since they are not reliant on TA Executions, can freely burn TA on Stim Boost.
So again, as I said, I would strongly suggest playing around with both and finding what fits your comfort zone. For me, I feel comfortable with poking at range, then closing in for the kill when victory is certain. I always like having a way out, and I enjoy having a constant flow of damage. That and, I foresee a potential doom for a Concealment friends in the coming weeks. :[