If by first column you mean the first column from your datatable (and not the row header column), then setting the CellType = "PushButton" does not display the CellValue property. A pushButton cell gets its display text from the style.Description. So, that is probably why you are seeing a push button with no text if that is in fact what you are seeing.
One way you can try to handle this is to subscribe to the PrepareviewStyleInfo event. In the handler try code similar to
if(e.RowIndex > 0 && e.ColIndex == 1)
{
e.Style.CellType = "PushButton";
e.Style.Description = e.Style.Text;
}
This should display the pushbutton and use teh style.Text property for the Description. If it does not work form PrepareViewStyleInfo, try it from grid.Model.QueryCellInfo.