Are All range hoods vented to the outside?
Keeping this in consideration, how do I know if my range hood vents outside?
It's possible, though, that the range hood is vented straight through the wall to the outside. To tell if that's the case, go outside and look at the wall to see if there's a wall cap to allow the vented air to escape. Of course, if the range hood isn't mounted on an outside wall, it probably wont' be vented like this.
Similarly, do range hoods have to be vented outside?
Since they don't need to vent to your home's exterior and are ductless, you are not required to install them only where there is a duct. These hoods operate by filtering the air they suck in and then blowing it back out into the room, essentially using a recirculation process.
It's never okay to vent directly into the attic EVEN IF you're attic is vented. Most municipalities require extractor and exhaust fans to be vented to the outside of the building with an vent cap. Excessive moisture will cause condensation on roof members and insulation.