Is there a way to pull a value or list of values into adobe from an MS SQL db? Perhaps a list of registered users that changes over time, but where I can group by date or hour and use the time dimension to segment data and summarize?
There are definitely ways to import data into Analytics. You may want to look into Data Sources (specifically Summary Data Sources) regarding your query.
Cautionary note, is to always test Data Sources in dev. The data once imported cannot be removed.