Zacate isn't Atom, as well as a Atom 330 isn't a 525 and they have different max temps, 100ºC for the 525, so what might be fine for X CPU probably won't be for Y CPU.
For example, a P 2160 has max temp of 73.3º but I've tortured several of them to around 100º, this is only because it has little and none thermal safeguards, the architecture and node helps also, thanks to that I have the world record OC with that CPU in air and mixed results under LN2 being always in top10. Anyway, if you try to do the same with for example a C2D 7400 you are in a hard road, iv'e toasted one (not my first or last) in the process of pushing it as far as I could, the max temp is 74.1º and they hardly can get stable at 90º. Then take a core i7 870, max temp 72.7º, with luck you can get 75º without getting a shutdown immediately and at 70º almost every time unstable, they have proper thermal monitoring, not like a Pentium or a CD2. So what's the point of all this, simply that as you get more up to date tech/cpus they have better thermal monitoring and don't get pass the specs given by manufacture.
Also, if you push an electrical component to higher temps you will have more chances of errors and degradation of the component will be way higher, this happens even faster with every new node shrink/new architecture, almost all Pentiums I've had continue to OC at the same voltages without problems, C2D after 2 years of 24/7 presents degradation and Core i is a pain, they don't last a year, same applies to GPUs. So it's always recommended to run your whatever as low temp as you can. You might not notice this in the long run until a day you power up your pc and it can't boot to the OS without errors, you lower the clocks and voltages and then you can, running at stock specs you have little chance to see this happen, but hi temps will not help you.
All this said, Zacate is 40nm, it has a GPU on die and I feel pretty sure has pretty tight thermal parameters/monitoring. I've made some builds with Zacate (Asus and Asrock) at work, sadly didn't have the chance to test it extensible and push the little bastard, not even a little OC yet, as soon this boards arrives or a build is finish they rip them of my hands
Everything said is keeping in mind your hard will work for long time without problem.
HWMonitor gives you the chipset temp, depends in the mobo how its call, but usually is the first temp reading after the voltages, as you only have one chipset there should only one reading there, that should be the chipset.