You can su in the terminal without issue. Pretty sure that's the case with Salix as well. Think he is referring to "su being executed in any other way except directly from a terminal".
vsuper takes care of this nicely, and is what is used for gparted and gslapt in the menus.
ktsuss also works on vector but I prefer vsuper as it allows you to have the root password remembered by the system for the duration of the session.
If I remember right there was a problem with this "remembering" of the password during development of 7.1, but I think it was uelsk8s who ironed that one out.
At anyrate just try using
that should do the trick.