Only Eclipse version 3.2 and later versions support an index. DITA2Go produces the index from your DITA index entries, in the form of XML file index.xml with links to your HTML topic files. When EclipseVer=2 or later (see §21.2.2 Deciding where to locate configuration settings), DITA2Go includes a label attribute in each index entry.
At present the only configuration settings that apply to an Eclipse Help index are those you can specify for the plug-in manifest file; see §21.3.4.5 Specifying Eclipse Help index properties in plugin.xml. See also §16.5 Configuring index entries for Help systems.