Oooh, maybe? I've not really come across a slacker that actually uses the RPM function that Patrick includes as an option, so it's a possibility I guess?
As for something like apt for Slackers, I haven't come across anything, HOWEVER... You could look at something like www.linuxpackages.net
for updated packages, and maybe setup an intricate system of cron and pkgtool/installpkg of some sort to check against versions and update??? I know there's a few threads about people doing different things like this...
Another option might be to look at distro's that are like slack, but include features that you want, I've been lurking around:
lately and they seem to be exactly that. it's slackware, optimized for i686, and includes a sorta apt feature. It might be worth your time to check it out.