There's some details about your environment that we would likely want to clarify, but generally speaking you will want to use GeoEvent Server to apply real-time adds or updates to a feature service whose underlying data source references tables in your SQL database (more or less). GeoEvent Server itself doesn't make a direct connection to any sort of databases. Rather, it uses user-configured server connections (ArcGIS Online, ArcGIS Enterprise, ArcGIS Server), and the map/feature services available from those connections, to facilitate adds/updates to the underlying databases registered with those 'servers' (e.g. the ArcGIS Data Store as a managed database, SQL Server as a database, Oracle as a database, hosted in ArcGIS Online, etc). In brief, adding, removing, or updating data is handled through the feature services which expose the underlying data in a database.
I am not familiar with the ins and outs of your environment, but generally speaking I could see a hypothetical workflow here where you create a registered server connection in GeoEvent that points to your ArcGIS Enterprise. From there, you can publish feature services (or use existing feature services) which reference some sort of enterprise geodatabase, like SQL in your case, that has already been configured with your ArcGIS Enterprise's hosting server. As real-time information comes into GeoEvent Server about your snow plows, you can set up GeoEvent Services to perform analysis on that data and then use that new information to apply updates to the feature service you published (which is essentially pointing back to a table in SQL).
One thing you mentioned was creating spatial views between the event features and the street line in SQL to then publish a street service symbolized by treatment time. While this is certainly a possibility, it is worth pointing out that this type of problem can be solved directly within a GeoEvent Service using its analytic capabilities. For example, it wouldn't be a far fetched idea to regularly poll buffered street data (lets say every 5 seconds) as the event features. Snow plows could be brought into the same GeoEvent Service as dynamic point geofences. Using a spatial filter, the buffered street segments could be evaluated every 5 seconds to see if they "contain" any snow plow. Assuming a street segment "contains" a snowplow, we can configure the next process of our GeoEvent Service to update the status of that street to "recently cleared in the last..." since the intersection occurred with the snow plow. The output of this hypothetical service would be your streets data with an updated treatment status attribute in real-time. If you were using this output to update a feature service, and that feature service was already in a web map, you could visualize the real-time treatment status of your roads based on a symbology that uses the changing field. We can fine tune other aspects of our analysis to account for time, road segmentation, whether or not the plow has its arm down, etc, but I wanted to throw this out there to demonstrate one of many potential approaches to this problem.
Some of this might sound like jargon if you're new to GeoEvent Server and that's okay. If you are new to GeoEvent Server, I would recommend working through the introductory tutorial series found here. It'll give you a better idea of how GeoEvent Server works and how it fits into the broader ArcGIS Enterprise.
