Generally speaking reverse thrust only reduces the wear on the brakes by allowing the use of a lower braking force. The actual "legal" performance of the aircraft is calculated without the use of reverse thrust and purely based on what energy the wheel brakes can absorb. To summise without reverse thrust the aircraft is more than capable of stopping in the required distance.
Actually the 737NG FAA certified landing data allows for use of partial reverse (1 eng credit worth I think) when landing on runways with less than normal (ie GOOD) braking. Of course if an MEL item exists on the reversers then the credit is not allowed.
Certification rules are not cast in stone so whatever the manufacturer can propose to the certifying authority and convince them that it is equally safe they can accept and put in the type cert documents.