I do remember that advice. I think that's an old recommendation meant to emphasize that in most of the cases the application should not try to do extra thread management for the container (the key word here is "container"). Also messing up with threads might lead to over utilizing the resources of your server. In the days of single/dual-cores that was quite important.
Anyways, today we have:
- more cores
- more applications that use an asynchronous model
The DataStax driver allows you to configure the max thread pool sizes so you can keep things under your control.
Concluding, I think it should be pretty safe to use the driver. You can tune the thread pool according to your app needs and server(s) resources.