C# does Datatable.acceptchanges() save changes to the actual database ?

NO!


http://msdn.microsoft.com/en-us/library/system.data.datatable.acceptchanges.aspx

When AcceptChanges is called, any DataRow object still in edit mode successfully ends its edits. The DataRowState also changes: all Added and Modified rows become Unchanged, and Deleted rows are removed.
The AcceptChanges method is generally called on a DataTable after you attempt to update the DataSet using the DbDataAdapter.Update method.

So your actual database is unaffected.