Baro-VNAV procedure design includes a height loss margin, and the minima are available as a DA/H. CDA approaches without VNAV guidance coded into the database do not qualify.
Adding an arbitary 50' to an MDA is just that - arbitary. The PANS OPS height loss margins for a pressure altimeter are as follows: Cat A 130', Cat B 142'. Cat C 150', Cat D 161'