Well, for RepeatingView the ids have to be unique for all components inside the repeater only.
The toolbars needs globally unique ids because it's not sure in which dataTable the toolbar is going to be put in.
Regarding long running systems:
Actually you'd have to create a lot of toolbars and put them in a single dataTable to run into duplicate ids. Apart from that there's no problem if the counter overflows - you'll just get negative ids.