It is probably pointless to debate this because the thing will probably pull a small cart once or twice a year however
a) My dealer is the one who sold and installed my hitch
b) My dealer said a small cart will be just fine on this machine and it is best to keep it under 200 lbs
c) The warranty does not list any towing exclusions. The manual does not mention towing at all. The hitch manual is the only thing that references towing and says 80 lbs.
e) I cannot see how me towing two 80 lb bags of concrete is much different than a 300 lb person riding the ZTR towing nothing. Provided I would be towing with a four wheel cart because I'd rather keep the front wheels on the ground.
In the end it is just going to have to be a calculated risk. The way I see it towing is fine in moderation, with reasonable loads, and with loads spaced enough to prevent overheating.
If you think towing is bad for a ztr, how about plowing?
Plowing 12" of snow with MiBar Plow and Ariens Zoom 42 Zero Turn Mower - YouTube
I would never do that! Now the snow blower attachments are tempting but I doubt my machine could handle something as wide as its wheels plus the salt would eat my mower alive.