Yes. And actually, if you have them ready whilst you are doing you final render you can push them in to the wall a bit to make them absolutely flush. Also make sure to tilt the vent forward a bit to make sure that any water landing on top will fall away from the wall and not drain back behind the vent, collecting and making the wall wet.
Whilst you are building the wall, make sure to remember to fit your vent properly, or you have to do a lot of chiselling to make that tube hole through hard cob. As I mentioned above, when applying your final outside render, push the vent into the wall to create an indent so the vent is flush in to the wall. Push more at the bottom so the vent is sloped and rain falls off the front away from the wall.
Mark and drill your holes for your wall plugs. If you have built your vent tube in to the wall you should not have any problems right now as the cob around the vent should be strong, but if you had to cut away your wall and fit the vent in afterwards then the cob may not be so strong and you may be relying on one or two strong plugs rather than all four. This shouldnt be a problem as the vent case is light can hold on with just one screw.
I would recommend using a drill bit that is the same width as the smallest part of the plug so it is really tight in there. The cob can sometimes fall away a bit so if you are using a bigger dril bit, you risk pulling away too much cob. Put your plugs in next
Use a screw that fits well in the plugs, do not over tighten.
And there you have it, a beautifully flush vent fitted directly to a natural earthen wall.