I can explain how Calibre DRC will handle it but someone else should explain the layer properties file ( I don't use it often enough myself)
For Calibre the default behavior is to use ALL the datatypes on a layer. Another way to think of that is that Calibre "ignores" datatype numbers by default and only focuses on layer numbers regardless of datatype.
So it might be interesting to see in DESIGNrev why do you have some things on datatype 1 ?
If you're certain that all the data on layer 31 is metal regardless of datatype then you can simply use something like this for the metal layer in the SVRF rulefile:
LAYER MET1 31
Now if you decide that the geometry on layer 31 with datatype 1 isn't really good metal after all, then you would use LAYER MAP within the SVRF rulefile to "separate it away" from the rest of the data on layer 31 (that probably has datatype 0 by default). There will be more details in the SVRF manual for "LAYER MAP"