There are various ways to get infinite and infinitesimal utility. But they don't matter in practice. Everything but the most infinite potential producer of utility will only matter as a tie breaker, which will occur with probability zero.

Cardinal numbers also wouldn't work well even as infinite numbers go. You can't have a set with half an element, or with a negative number of elements. And is there a difference between a 50% chance of uncountable utilons and a 100% chance?