A lot of people, men and women like strong sensation on their nipples. It's arousing to them, and for many of us, the nipple play paves the way to coming.
Some clamps also can be used on the labia or other sensitive body parts. I am not sure about these bull nose clamps, as I do not have this set.
However, when I think of the word "fetish" I think of the psychological definition, meaning "something unusual one needs in order to become aroused." Needing penis or clit stimulation is not a fetish. Needing to lick a shoe or wear panty hose, or have your partner wear a bright red clown nose in order to get turned on IS.
So, no, these are not "a fetish" but they are very arousing to many and a LOT of fun.