I have never seen or heard of anybody doing that to a Mosin, if it is the carbine length Mosin then you will need a very hefty reddot to handle the recoil. Most i have seen have been done with the scout scope mount replacing the rear sights and using a long eye relief scope
I have the scout mount on my 91/30. While I was waiting for my long eye relief scope to come in I was messing around and put the red dot on it. I honestly don't think it would hold up to the recoil plus it looked absolutely ridiculous. I now have a 2-7x30 long eye relief scope on it that I love. I ended up putting the ATI stock on it as well so I wouldn't feel bad about beating up the stock a bit.
As stated, a cheap reddot probably won't stand up to the recoil. If you bought a nice one, like the ones some trap shooters use, then maybe... but then you are spending 300 dollars on a scope for a 75 dollar rifle.