The link between Identity Mixer and UMA is through the digital wallet. My pre-UMA digital wallet is 1Password. I wish it were on-line and able to service some authorization requests autonomously in the sense that UMA allows some OAuth authorizations to be serviced while I'm asleep.
Here's the Venn diagram form
http://openid.net/wg/heart/ showing three kinds of actors:

Notice that UMA is personal technology linked to an individual, whereas OAuth2 is linked to relying institutions, and OIDC is the federation actor.
My digital wallet will reference identity federations and provide attributes that inform both the UMA and the institutional actors. To the extent my digital wallet is also a personal data or attribute store Identity Mixer or uProve technology would be a huge benefit.