Just to completely cap this from the point of my own input on the subject (it's already capped in reality per the devs) I was still struggling with memories of stacking these at some point and also some information I found from later years that claims they do stack.
So I hunted around some more and found even more evidence that Uth is dead nuts right. A link from July 2001 EQ Casters Realm also indisputably says that Druid dots from the same line (i.e. swarm, crud, etc.) do not stack. Link here:
http://web.archive.org/web/200109111...ons.asp?Id=909
Bottom line, in Classic EQ they did not stack, so they aren't gonna stack here. Kudos to Uth for knowing this, implementing it, and standing up politely in the face of being questioned while still sticking to his guns.