If you can lookup how to capture info from a command prompt and put it into a table, you could use the command:

Net start

To list all running processes. Joined with the the info from the registry, you cab figure out the started and stopped versions of SQL.

If you want to keep it all in the registry, they key will be something like

Hklm\services\control\current version\mssql(instance)

(^^^ the above key is not correct as I'm not near a windows PC to check. It is approximately right.)

This will give you the actual status of each service, e.g. start, stopped, paused (probably numeric values for each). Overkill?

If it were me, I'd use the net start command as I don't need to list all the registry keys and then search its values.