Does the 15% chance to devour and instant kill work if entangled? Similarly, does 4x+ skull matches do the same? According to the card descriptions, 4x and 5x while entangled should work, but 3x while entangled shouldn’t.
It does. I just Spring Imp’d a Great Maw, thinking that would protect me.
One 3-Skull match later, my Gorgotha became dinner. 
Have you tried it with Archer? It makes sense that The Great Maw does for it is a 15% chance to trigger devour. Devour isn’t reduced by entangle. The difference with Archer is that it does damage, shown by the fact that archer dies to 50% Gloom Leaf return damage.
I have not.
True, but the trait description states a 15% chance on skull damage,
hence my belief that zero damage would equate to Hunger immunity.
Yeah, I initially though that too, until I noticed how the hunger trait behaves with Gloom Leaf and skull glitch effects. The skull glitch effect being shown below:
It has the same problem like other effects in which it spams like crazy. This also likely means things like burn, freeze, and other effects on skulls also work through entangle.