Historically Halloween isn't as crowded as other late month nights but it's still busy. If you can be at the gates to get in line around 5pm, you should stand a good chance of doing more than two houses w/o Express passes. At this point...it's only a guess though.
lisareneeo, we'll be there too that night! The people at Universal confirmed what the PP said: that Halloween night is traditionally not as crowded and they're expecting a lighter crowd because Halloween is on a Sunday night this year.