It's always nice if some one makes life easy for you. 😎
As always, adding default values for columns is something that depends on the needs of your data model !
If your DA agreed on only having defaults defined for some columns and a DBA wants to add them anyways, he (the DBA!) should give that feedback to the DA and get it approved !
With your staging db, rules may defer from the actual OLTP db because you are preparing stuff for later purposes.
Then adding defaults may ease tool usage to load data into a DWH, because in many cases NULL isn't an option.
Also in this case, double check with your DWH-DA to be sure you are providing the correct adjustments.
Keep in mind, when adding a default value, it doesn't alter the actual current content of the column !