True also but note that you won't be disadvantaged by doing well in straight Commerce and it's also much harder to "do well" in Comm/Law in the conventional sense. ie HD average in Comm/Law.
Essentially there's really no need to risk it if you are not interested in Law at all.
Seremify makes a valid point about doing com/law. Law isn't just learning about the law and the legal system. It is a degree which promotes critical thinking and works your mind. The skills required to study law help those who will move into front office because of how it makes you think better. Why do you think a large chunk of law graduates don't practice? They use the degree for what it provides which is a highly mentally stimulating degree.
Bearing this in mind this cadetship would much favour single degree students. They are more flexible than those accounting cadetships but they do favour single degrees because of the contact hours. To anyone who gets offered a cadetship with UBS they will understand why, work takes up a large chunk of potential class time and the leave entitlements differ.
Furthermore people in this forum need to understand the UBS cadetship is not a front office role. If you think that's what it is and that's all you want to do you won't last. People make careers in the back office. Whilst it is a good framework for a potential front office role, you need to respect the cadetship and job for what it is by working hard in the back office work it entails. UBS is an excellent place to work but make sure you know exactly what is involved.