@schang That should work. I can confirm that on my end I was able to take a dataset and plot it on the scatter plot. I am seeing some odd behavior though where the tooltip will briefly display and almost immediately disappear when I hover over it. This issue is intermittent so not sure what's the reason. It appears to be a UX bug (at least for me). I'm running DSS 8.0.0. As far as the functionality goes, though I am able to display both numerical and string values within the tooltip - its just that they do not render on screen consistently.
This is probably a foolish question, but you have tried hovering over the data point with your mouse, right? Are you having an issue different than the (apparent) issue I stumbled upon trying to recreate your issue?