You have to check the blob field in the Fields tab of the layer's properties. This way you'll be able to see that the blob field is there when you do an Identify or bring up the attribute table. But you will not be able to see what's inside the blob field. ArcMap does not handle blob field because in a blob field you can keep any binary data (a pdf, a doc, a picture, an mp3 etc). If you want to see in ArcMap photos from a blob field or save pictures from ArcMap in a blob field, you'll have to develop your own functionality to do that (in ArcObjects)