"Indicator" simply means display, in this case the rotating cathode-ray display for radar you see in old movies. Rebuilding it to be a 'scope as they suggest would be possible.
Nope, it certainly wouldn't be the rotating radar type display. The tube is the totally the wrong type. This unit had a standard 3BP1 tube in it which is a 3" tube with electrostatic H and V deflection plates and the standard P1 green phosphor that has relatively short persistence used on early oscilliscopes and computer monitors.
Many radar tubes would need a longer persistence phosphor, though the "rotating" ones you're thinking of (like a 3CP1, introduced in 1941 which is electrically the same as a 3EP1 but with the radial deflection electrode, or the later 3DP1 which is otherwise electrically the same as the 3BP1) have the same normal green P1 phosphor but are constructed differently than X/Y tubes with their horizontal and vertical plates and instead have a radial deflection electrode.
From Peter Keller's "The Cathode-Ray Tube" book:
3BP1 - RCA announced the three-inch 3BP1 (Figure 4.16) in January 1943 as being available for WPB (War Production Board) rated orders. The most significant feature was the large 14-pin diheptal base which was designed to permit operation at higher anode voltages and altitudes without high-voltage breakdown between pins. The 3BP1 was used for a number of oscilliscope, radar and aircraft in-flight engine analyzer applications. Wartime 3BP1s manufactured by RCA, Du Mont, Norelco, National Union and Sylvania still may be found in the electronic surplus market and a 1945 advertisement by General Electric also lists it as part of their product line. The 3BP1A with its improved electron gun was still being manufactured for military replacements as recently as 1988 by Thompson-CSF (now a part of Hughes Aircraft).