Hi Riccardo,
this is an interesting speculation, however consider that 1-vinylpyrrolidin-2-one itself is clearly carcinogenic in rats:
1-Vinyl-2-Pyrrolidinone Summary Risk Assessment Report (ECHA)
In fact it was limited below 10 ppm in the harmonized monograph (Ph.Eur, USP-NF, JP) on Povidone.
Even if all the content will undergo hydrolysis to give 4-(vinylamino)butanoic acid and assuming that part of this will be nitrosated to give 4-(nitroso(vinyl)amino)butanoic acid, I do not think that these traces of nitroso impurity may significantly increase the risk of cancer related to 1-Vinyl-2-Pyrrolidinone.
Kind regards