I would say almost certainly yes. In my own forum I found that a short period after I had implemented spam filtering, the moderation queue length (everything that gets rejected as spam goes in to the mod queue) had very little spam in it. I would surmise that spam bots are at least smart enough to check that their posts are getting through, and if not, don't waste time posting content (just try one every now and then to see if you can slip one through and then hammer it!).
