if you have abstract urls enabled I don't think the server cares what you set for directory file. It looks to me like any index.* file will be served.
There is code so that you can set directorylisting "none" and the index file will not be shown but it doesn't work without the following change.
change the following line in ad-abstract-url.tcl from
if { [string compare $listings "fancy"] || [string compare $listings "simple"] } {
to
if { [string match $listings "fancy"] || [string match $listings "simple"] } {
then "ns_param directorylisting none" in the "ns/server/${server}" section of your config file should work fine
