Highlight just the class:  &:not(.nohover):hover {

Technically this regexp is far from adequate, but practically, this is sufficient with the goal of: allowing almost any character in class names (per the spec) and making this function style syntax work without making the tmLanguage overly-complicated.

An aside: this would be way easier if TextMate allowed proper tokenizing parsing. But I probably don't know what I am talking about.