i fear that is not possible to do on xfce. The applications provide this behavior. XFCE has in this case nothing to do with that. On the panel there is a an object called “indicator”, which is used for applications. XFCE just displays them. thats all. Same with notifications. If the program don’t provide that, then xfce cant display anything.
Maybe KDE works better there (because teamspeak uses the qt toolkit), idk , but i don’t use it anyway. I prefer Gnome or XFCE, or any GTK based DEs.