Using local allocators where they offer some benefit certainly is idiomatic C++. Freeing all objects so allocated by simply reclaiming the blocks from a local allocator is also idiomatic C++.

Major subsystems that use no memory except what is passed in from above is also idiomatic C++.

C++ is a big tent. Things you do routinely in one part of a program, such as at startup, may be very different from what you do in a main loop, or in termination cleanup. Things my program does may be very different from what your program does.