I believe that is known as "What's This" help. RoboHelp 2015 Release has an area for that. Click the Project tab and choose the Output Setup pod. In that pod is something called Context Sensitive Help. Expand that and you see What's This ? Help Files.
That's about as far as I can lead you. I'm only aware of their existence and how they work from an end user perspective. I've never created them myself.
For a client, I've created a custom workflow for this. They generate a WebHelp output. Using scripts, that WebHelp output is stripped down so that every topic only contains the tooltip help. The application reads the topics from disk and integrates them with the software.
As for an alternative: do your developers have a resource file that you can edit? Perhaps they have an XML for tooltips and you can simply provide them with the text. No further work for you.