Yes SSIS won't be able to return null value in a date time variable. Also I am not sure why its returning a particular date when the value is NULL.
I just have a work around for this (I used it in one of my pacakges). In the select query return some value in case the max(LastSuccessDate) is null.
SELECT COALESCE(MAX(LastSuccessDate),'1/1/1900' as minDate FROM TableStats
And in your packacge treat this returned value ('1/1/1900') for null case.
HTH
~Mukti