I have not noticed any additional sweating when in PEM per say.
But...things that are likely to cause PEM, such as working on something bent over, even when sitting, usually cause excessive dripping on whatever I'm working on. I have not noticed others experiencing the same thing.
I also have a tendency to sweat excessively, head and neck, sometimes upper chest, while unconscious due to being shut down because I've over done things.
It's difficult to say if these are as a result of PEM, as a lot of the time I am PEM'd.
It's also difficult to be sure due to the fact that I am overweight, not exactly fit, and 55.
I have not noticed people who are much larger than me sweating in situations where I have virtual rivers of the stuff coming off my head. Of course it's possible that even 25-30 stone people are much fitter than me so cope with the heat better.
Then of course there are those days when no matter what the heat where I either don't sweat or hardly do so - when I knew people, and went out, it used to bug the hell out of couple of them that they could be melting and I was perfectly comfortable and not sweating. The same guy who basically sat unmoving and sweated heavily for hours when they were perfectly comfortable or even cold, after traveling to their homes
So no idea if in my case sweating and PEM are connected in a simple manner or if it's just me being me.