Great news! IBM UBX Capture and DDX are entirely compatible! Here is how tagging will work when you use IBM UBX Capture.
When IBM UBX Capture enables IBM Digital Analytics, DDX tagging is included automatically. Be aware that for an IBM UBX Capture enablement, the library for the enabled application is loaded and DDX does not need to deploy any Partner Library enablement tagging for the application. As you enable tagging in oneSDK, the same tags should be removed in DDX. Similarly, as you add new partners to IBM UBX Capture, their library loads have to be removed from DDS.
You can use IBM UBX Capture to load Tealeaf and idSync as well and still load vendors with DDX and use it for tagging. Using IBM UBX Capture and Tealeaf in conjunction gives you the benefit of a common session ID.
IBM UBX Capture cannot migrate data from DDX as of now. Note that IBM UBX Capture always loads DDX when it loads IBM Digital Analytics. This means that you can migrate your data whenever you get a chance.