interesting......however....
unfortunatly the only one who can decide if they are VFR or IFR is the pilot and even the best met actual or forecast cannot tell you exactly what the weather is doing at that precise time in that bit of air.....
i do feel for you however the pilot flying VFR could have been flying round the clouds etc, there may have been gaps etc.
i honestly dont feel there could be any recourse in this matter unless the weather was so bad but then if it was that bad he would have to have been given a SVFR clearance so it couldnt have been too bad?
sorry