You can run multiple Vendor Databases with Snapshot
Let's take ABM as a Vendor - let's describe the options:
If it is NOT required to have multiple ABM databases be used in Snapshot simultaneously by users (in other words only one ABM database to be accessed at a time by all users) then you can just have one install of Snapshot and change the ABM database on the settings screen (Update Business system Database Connection) of Snapshot, then check for new dashboards to make sure all views are up to date for the ABM database.
If you wish to have multiple ABM databases accessed at the same time then you will require an install of Snapshot into their own directories using the Stand alone mode per instance of ABM database. This will also require a Snapshot database per install and a licence per install. There is a file that will be located in each install folder based on the Stand alone setting that stores which Snapshot database to be used and it's the Snapshot database that stores the connected ABM database and dashboards for that database.
Databases other than a supported business system.
This will require using a Snapshot setup that logs into one of the ABM databases as Snapshot requires a business system type and a database to be selected. Once in Snapshot you can make use of the Custom Connection strings to connect into any other database. Custom dashboards can then be created using the custom connection string.