Yup I used to run one on my Speed6. They are great buuuuuut there are some things to consider:
There was a big overhaul to the valve cover design for the Mazdaspeed3 to make the valve cover breather tube closer to the turbo inlet pipe to increase pressure, evacuation. A lot of users were burning oil at idle due to improper manifold pressure, issues with turbo oil seals causing the car to suck up more oil in the intake path and also for oil to get past the turbo and get burnt in the exhaust.
Ideally, if you could put an OCC inline and not mess with the pressure you'd be golden. Not a bad idea but there has been a lot of man hours to make sure the car non boosted performs properly in relation with the pcv valve and valve cover breather.
2012 SGM Ti DCT Stock and loving it
OEM multispoke 17" with stock rubber summer-X-ice 3's on stuck rims = awesomesauce