I've had this done to me before, one memorable game, I was undead and tried to Dreadlord fast expand on Plunder Isle. A keeper of the grove kept up hit and run attacks with entangle, every time I slept him he was just at the edge of range, and didnt have enough ghouls to surround. Sure enough, about 4 minutes later 5 or so ancient protectors walk into range of my base and take root. I go to try and kill them with my ghouls and some skeletons, to find them backed up by half a dozen archers and that damn keeper. Every time I tried to engage, I lost a couple ghouls to focus fire, and another one to entangle. I quit after about 40 seconds of that crap. To summarize - if your better than your opponent it will work fine, if not, it might work, but it is not the same thing as a human or orc tower rush.
offtopic: Why do I not see any threads in this forum until I post in it? Are my settings just screwed up or something?