Slickgrid view settings does not provide an option for Inline Cell editor for non-integer numbers. The following hack to the file slickgrid.module in the function slickgrid_get_plugin_options_for_field(...) works but is obviously not the right solution:

if ($field_type === 'number_unformatted') {
  $field_type = 'number_integer';
}

Otherwise, the slickgrid plugin is awesome!