Understanding Mixpanel's Identity Merging with Segment Properties

Hi all, I'm wondering how Mixpanel uses properties sent across from Segment through the Import API. Usually Segment passes an anonymous ID which is used as a user's distinct ID in Mixpanel. This doesn't really allow for cross-domain identity merging if one domain (A) uses Segment + Mixpanel Imports and another domain (B) only uses default Mixpanel autocapture setting. If I take the device ID generated by Mixpanel from domain (B), then put that into the Segment contexts on domain (A) and have it be mapped so that it's sent to Mixpanel under device_id, then a user logs in and identifies on domain A, will Mixpanel know to use that Device ID to merge the identities?