I only put them on the payload section for the main. You should have a friction fit on your coupler enough so if you turn the rocket upside down it would keep together, but it is still easy enough to separate that it can deploy easily.
I've seen some RSOs turn rockets upside down before signing off on them.
The point is, shear pins shouldn't be necessary on the drogue side. That is, unless you have a more complex arrangement such as with air starts or multiple stages.
That being said, shear pins aren't going to hurt anything if it makes you feel better about it. As long as you ground test to make sure your charge is enough to break the pins.
If I could give one tip for shear pins, it would be to invest in a #2 tap. Makes it much easier to get them in w/o making the hole too big.