Yes. Although ArcGIS Online: Types (Unique symbols) states there is an absolute limit of 200 unique values with 10 unique colors to differentiate the types of categorical data, it is possible for Map Viewer to display datasets with more than the set limit of unique values and colors.
The limitation only applies when creating a layer style through ArcGIS Online Map Viewer. When a style is created for a dataset with more than 200 unique values in Map Viewer, the remaining values are placed under the 'Other' category, with 10 colors representing the multiple categories. For example, the image below shows the layer has more than 200 unique values but is represented by only 10 colors when using Change Style in Map Viewer.
However, datasets can have more than 200 unique values or 10 unique colors in ArcGIS Pro or ArcMap. The image below shows the layer has more than 200 unique values and is represented by more than 10 colors.