The false cases of domestic violence or dowry harassment offences are not the exclusive properties of inter case marriage and disputes at a later date.
First of all it is our wrong notion to think about a DV case just because your son is planning to get married to other caste girl. What is the basis for this belief?
Instead of having a negative approach to this subject, why dont you think it otherwise i.e., by giving your consent for their love marriage, being them to your home and shower your affection on her as you do on your son, if this happens, there wont be any reason for a DV case or any other false complaint on you or your family members.
Better attend the marriage, bless the newly married couple, ring them home,, allow them to stay peacefully in your home as long as they would decide or desire to stay there, after that you can arrange a separate home for them by which you can avoid the possible rubbings which you are afraid may lead to a DV or any other criminal complaint.