With the latest patch Steel Tornado is undodgeable because it’s AoE. It remains blockable though.

I don’t think poisons can crit, but I don’t know for sure - I don’t use them.

From the most recent patchntes:

Block & Dodge Rulesets

We’ve updated several abilities so they better adhere to our block and dodge mechanics. The system is set up to be intuitive – attacks on the ground such as fire or Caltrops cannot be blocked or dodged. We also want dodging to be useful during some instances, and blocking to be useful at other times. The ruleset is as follows:

Attacks that can be blocked, but not dodged
AoE explosions such as Radial Sweep, Spear Shards’ initial hit, or Drain Power.
Beam attacks such as Radiant Destruction, Lightning Staff, or Soul Strike.

Attacks that cannot be blocked or dodged
Damage on the ground such as Wall of Elements, Caltrops, or Lightning Splash.
Effects that are on or inside a player character, such as Daedric Curse, or Backlash. (Damage over time effects)

Attacks that can be dodged, but not blocked
Secondary effects that penetrate Block such as the Damage over Time from Sunfire, the surprise attack armor debuff, or the snare from Low Slash snare.

Note: Block continues to provide stun immunity, so it will stop a secondary effect like the stun from Stonefist.
Exceptions to these rules will be stated each ability’s tooltip, such as Fiery Grip which cannot be dodged or reflected.