Do you need sales experience to be a successful sales manager? If not, what skills or experience do you look for in potential sales managers?

I suggest that the answer is a bit more nuanced. I think good sale managers (and some of the best) actually comes from other functions that are sales adjacent. Sales Enablement, Account Team Finance, or Strategy and Execution roles are all disciplines that are close enough to sales that they could be solid candidates. These types of candidates would also need to be quick studies who can demonstrate the ability to jump into new assignments and quickly learn how to perform. This transition is not an easy route, but the long-term benefits of having someone with a different skillset and diversity of thought in the sales management ranks can be quite beneficial for the leadership team.

You don't necessarily need a lot of it, or to be the top sales rep, but I don't believe having spent time in the trenches is important. 

It's hard to help somebody along if you don't understand the situation they're in.