This is not really clear from the website. Mixpanel is mentioned in https://jitsu.com/sources but NOT in https://jitsu.com/destinations. Also the docs seem very clear about that.

We are currently looking at Segment, Jitsu and others. While we generally liked Jitsu, this was kind of a big deal for us and made us lean towards Segment.

However, no final decision has been made yet. ;-)