I would suggest that you look at the section titled "Dynamic Indexes for Indexed Properties" at this link:
http://struts.apache.org/1.x/struts-taglib/indexedprops.html It shows how to build the indexes using some scriptlet code. I am pretty sure you will have to do it this way instead of using the index attribute. You will need to build up a property value that looks something like:
"MyObject1[0]. MyObject2[0]. MyObject3[0].value"
- Brent