[Edi]

Heroes are not unique, but only appear once because they have been designated as national heroes by the #hero1-5 command. IF they die, you could wish for them again and get a shiny new one. If you have a summoning spell, e.g. Abysia could summon 15x Ba'al Chozron and Sauromatia as many Circes as it liked and so on. So making them summonable is a bad idea.

By the way, if you haven't been around, there's a new reorganized modding manual out as a result of a project of mine. Thought you could find that useful. You can find it by following the link in my sig.