Cloud-like spells vs Blindsight

[flappeercraft]

So on the fog cloud spell it says that creatures within 5 feet get 20% concealment and further than 5 feet get 50% concealment. It also says that it obscures all sight but according to the SRD blindsight is using a nonvisual sense. Would this allow a caster immune to poison to be inside the cloudkill as a defense and have no penalty within the reach of his blindsight?

[Necroticplague]

So on the fog cloud spell it says that creatures within 5 feet get 20% concealment and further than 5 feet get 50% concealment. It also says that it obscures all sight but according to the SRD blindsight is using a nonvisual sense. Would this allow a caster immune to poison to be inside the cloudkill as a defense and have no penalty within the reach of his blindsight?

Yes.

Using nonvisual senses, such as sensitivity to vibrations, keen smell, acute hearing, or echolocation, a creature with blindsight maneuvers and fights as well as a sighted creature. Invisibility, darkness, and most kinds of concealment are irrelevant, though the creature must have line of effect to a creature or object to discern that creature or object. The ability’s range is specified in the creature’s descriptive text. The creature usually does not need to make Spot or Listen checks to notice creatures within range of its blindsight ability. Unless noted otherwise, blindsight is continuous, and the creature need do nothing to use it. Some forms of blindsight, however, must be triggered as a free action. If so, this is noted in the creature’s description. If a creature must trigger its blindsight ability, the creature gains the benefits of blindsight only during its turn.

Blindsight never allows a creature to distinguish color or visual contrast. A creature cannot read with blindsight.
Blindsight does not subject a creature to gaze attacks (even though darkvision does).
Blinding attacks do not penalize creatures using blindsight.
Deafening attacks thwart blindsight if it relies on hearing.
Blindsight works underwater but not in a vacuum.
Blindsight negates displacement and blur effects.

If it's concealment and doesn't say otherwise, blindsight lets you ignore it.

[Duke of Urrel]

If your Blindsight were based upon the sense of smell and the cloud used was the Stinking Cloud, I would rule that the stench of the Stinking Cloud would make it hard to smell anything else, thereby reducing your Blindsight to the Scent ability. (I would consider the Stinking Cloud to negate the Scent ability completely.)

But with the Cloudkill spell (and poison immunity), I think you're all right, regardless of how your Blindsight works.