Matt,
I'm gonna have to go dark for the rest of the day, but I'm wondering if there is something up with your asset package (potentially an older version of the model?). Check out my screenshots from earlier in the morning and you'll see that the "globalid" field in the target asset packaqge should be a guid data type and not a globalid data type, this is what allows the data loading workspace to bring your source globalid into the asset package. in your asset package your globalid field is a globalid data type, which means the data loading workspace cannot populate it. I would recommend you download and use the latest Esri Asset Package ( Water Distribution Utility Network Foundation | ArcGIS Solutions for Water ), as the asset package included in the sample data loading workspace appears to be using an older model that doesn't allow for carrying over globalids.
Note: there may be some adjustments you need to make to your data loading workspace if there are some model changes between releases. I did have to make a few changes, but I believe all of mine were related to source data issues.
Once you have global ids coming across, then getting your related records over should be (relatively) simple. As simple as anything that involves GIS and python can be expected to be.