You may be aware, but nautilus-gksu is available in squeeze. The dependencies look ok, so you
could just repack it to install to the extensions-3.0 directory (or you could grab the source and just rebuild it properly). You certainly don't need the 'buntu package.
As for security concerns - it's not being developed so the risk is all yours. You may want to read
https://bugzilla.gnome.org/show_bug.cgi?id=654184
http://packages.qa.debian.org/g/gksu...0T171717Z.html
Or to cut a long story short - "nautilus should not be run as root"