They do practically guarantee that flammable gases/vapors will enter an explosionproof enclosure. Then again, the flammable gases/vapors will enter through any threaded connection anyway, with or without a drain/breather, which is why I usually avoid them.
That said, a drain/breather identified for Class I does not usually "compromise" the enclosure. The exception is salt-air applications where residue build up may (only may) defeat the spring. Personally, I've never had that happen.