I have heard that using a tire with an aramid bead on an old non-hook
rim is a bad idea. Is this true? If so, could someone explain to me
how the aramid bead behaves differantly than a steel bead?

Also, what exactly is the purpose of the "hook?" Is this documented
somewhere?

A google search of the group only turns up some vague references to
not use kevlar beads on non hook rims, but no explanation.