Baptism is the rite of the universal Church that incorporates a person into the mystical Body of Christ.
In the broadest sense, baptism provides if anything, that sacramental, concrete connection with the universal Catholic Church. However, Protestants are outside the active and sacramental participation as members in the Church.
Subsequently, we see the Protestants as our separated brethren. Their baptism is considered as valid. If they decide to become Catholic, at the discretion of the Pastor, after proper instruction and affirmation, they could be attending Mass the next day as full fledged members.