(This is why, as a DM, I hate Dragonfire Adept's, but anyway...)
I actually find Runestar's example to run counter to his point. To me, DR 10/magic implies the gaseous form is very hard to pin down without decent magic. That said, your last post confused me:
In the case of my entangling exhalation, which stipulates in slow breath's case, if they're slowed they're entangled as well then I'd say they can't shake it off.
For the entangling breath to work (I assume we're talking about the feat from Races of the Dragon), you have to do damage. The slow breath does no damage, so they're different and you can't use the entangling with the slow, so I'm not sure how anything is stipulated in "slow breath"... Not trying to be difficult, just trying to get onto the same page as you.
That said, I guess I would again go back to what I said before. If you go by raw, if you do damage, it is entangled. That is exactly what the Feat says. If the target is immune to the type of energy you're doing
or takes no damage at all from a non-energy based breath weaponl, then it's not entangled. If it does take damage, it is entangled. As a DM, I find the feat overpowered (
so also take this as full disclosure of some bias on my part), so I might be inclined to House Rule a gaseous form is able to slip out of it (maybe, as you say, with an escape artist check or something... maybe DC 10 + half damage) but that would not be RAW.