Unless you are on a realtime OS, you may see longer pauses from the OS due to scheduling other processes, so I think it's fair to consider the new low-latency collectors (Shenandoah, ZGC) pauseless from a practical point of view.
You can't call GC pauseless if it introduces pauses. We don't say something is free if you have to pay little for it. We say it's cheap.
I think as a technical term, pausless (as used here) has a specific meaning, just like real-time has a specific technical meaning (not literally 0 latency since that's generally physically impossible).