You can check the subsection "HTML representation" under the "Restful Web Service" section of the Virtual DataPort Administration Guide. As you can read there if you are using the HTML output you will be able to access a blob field only if the view has a primary key, and in this case it will do so through a link that will show the value of the field depending on the content type. If the view does not have a primary key then, as you say, it is not possible to request a blob value and the fields will be hidden.
You can try to set a primary key for the view that you are accessing through REST or, if this is not possible, try the XML or JSON representations. For more information about these representation check the same section of the Administration Guide.
Hope this helps!