В Grid dojo 1.5 нашел вот такое поле...
// rowHeight: Integer
// If rowHeight is set to a positive number, it will define the
height of the rows
// in pixels. This can provide a significant performance advantage,
since it
// eliminates the need to measure row sizes during rendering, which
is one
// the primary bottlenecks in the DataGrid's performance.
rowHeight: 0,