Joe,
Symbology by a single attribute is supported. I wanted to use multiple attributes, which is not supported. Basically, I wanted to use one field to set the shape of the symbol and a second field to set the color of the symbol. As a simple example, Field1 would contain either "circle", "square" or "triangle" and Field2 would contain either "yellow", "red" or "green".
However, since my set of symbols and colors is small (9 in my example), I can put them all in one field. Values 1-3 would use a circle, 4-6 a square and 7-9 a triangle. Then 1 would be a yellow circle, 2 a red circle and 3 a green circle., etc.
For a lot of colors and shapes, using two fields would better organize the choices for the user.
Thanks.