This is the reason why ASP.NET 2.0 membership exists, but it looks like a huge task to get DNN to use an other applications membership database. on the other hand it is a nobrainer to have a simpler application use one of DNN's "applications"

Microsft made it by design so that applications could interchange their userdata with just a little configuration. But it isn't that obvious with DNN. my own exploration in DNN membership seems to point out that DNN really needs at least 2 "applications" in terms of membership. One for the superusers, and one for each portal.