Dixie dean,
I went glacier ski-ing at Tignes (which I know is not Zermatt but I guess it would be similar) at the end of October last year. It was really sunny and hot, especially sitting out on the restaurant veranda where most people took off their outer ski wear, but on the snow it was quite cold. We used factor 30 suncream and sunglasses and we were fine.
There were some frightening looking small holes in the snow on the drag lift route, but I just skied over them and hoped for the best. I imagine it was safe enough really, but probably not too good if you have a 'thing' about falling into crevasses! The piste seemed to be fine.
The other strange thing about summer ski-ing, which you probably know already, is that the lifts open very early and close very early because the snow becomes slushy in the afternoon. First thing in the morning the snow is quite icy, then it's very good, and towards the end of the day it starts to get a bit soft. In fact, when I was there the snow had gone from part of the piste by late afternoon exposing the glacial ice.
I hope you have a great time - I did
Ally