Turbo seals and overspool aside... a properly setup catch-can is a good thing on any modded turbo car. Hell, they're good on un-modded turbo cars too if you're driving them hard.
I'm not totally sure how the PCV system works on the MS3, but on the WRX/STi there are two circuits that benefit from catch cans: the crank/pcv breather, and the valve cover breathers. They both vent into the intake so if you're pushing oil out them, you end up sucking it through the cold side of the turbo to be burned in the engine, which screws with the octane of the intake charge, not to mention messes up the turbo if there's a lot of oil. I'm sure the Mazda is similar, no?