If you're running AOLserver and PG on the same machine, chroot AOLserver and tell PG to only accept local host connections you should be in pretty good shape. If they can't hack OpenACS into submitted arbitrarily long queries then you shouldn't have to worry too much about buffer overruns in PG, at least.
Let's face it, if they get in and root you and want to ruin your day "rm", not "psql" will be the tool of choice. Still ... if they've not rooted you but just got into a user account via crack or the like, you'd be safer if psql were removed from your system altogether. You can do that once you've installed all your packages from the OpenACS4 APM.
The client library for PG does support encrypted communication. But opening up your db server to the net is asking for trouble, since you then would be vulnerable to any buffer overrun (or other) problems in the PG communications code.
