RE: Possible to use Traveler to sync with a Mail-In database
No. Traveler needs to be able to authenticate you as a user, and the MID doesn't really have a "user" assigned to it. Traveler has an existing enhancement request to add the capability to sync other databases (MID being one type of "other" databases), but it isn't there now.
Feedback response number RSSN985RWP created by Robert S Sielken on 05/28/2013