A DME arc can be used within an Arrival segment, or Initial Approach, or even Intermediate Approach. Pans Ops speeds are different for each performance category, of course, and might differ in each of these segments. I say "might differ" because, while the Intermediate segment has no specific speed limit, it is assumed that pilots will be slowing down from Initial approach speed to the Final approach speed in this segment.
In some countries, speed in any of these segments might be further restricted by local rules, or even modified by a restriction on the particular chart.
Rules relating to "being established" on the arc can differ from State to State, based on their own interpretation of the protection parameters in Pans Ops, or on other factors that might be unique to a particular State. Off hand, I think that Australia allows a pilot to be established when within 2NM of the nominal radius. Here in PNG, it's necessary to be within 1NM.
Hope this helps.