Nope. Spawn too many units, thats what happens. Mainly its the triggers initiating over the actual units being drawn that creates the lag. Perhaps if you spawn them in smaller groups, say, if you want to spawn 100 units, you can 10 every half second over a few seconds. Even if you spawn a large cluster, it will take a sec or two to get them all moving anyway, so you wont be losing much time.
-VGsatomi