You should use one of your group variables to feed the data to the table:
http://jsfiddle.net/djmartin_umich/3v68c/
var datatable = $('.table').dataTable({
"aaData" : dateDimTotal.top(Infinity),
"bDestroy": true,
"aoColumns": [
{ "mData": function(d) { return d.key; }, "sDefaultContent": ""},
{ "mData": function(d) { return d.value.count; }, "sDefaultContent": ""}
]
})