I checked my Jeppesen set for LIRF (Fiumicino). I only find DA for the RNAV approach to RWY 25 when using LNAV/VNAV with GPS or DME/DME or when using LNAV with GPS. Using LNAV wit DME/DME still is a MDA as for all the non precision approaches at LIRF.
The normal airliner way to fly NPA nowadays is using a continous descent approach (CDA). The CDA is flown like an ILS using the on board equipment. And yes you make the decision at the DA like for an ILS approach.
If you have a look at the RNAV approach chart for LIRF you will see that you reach the DA before the MAPt.