Can I use hook-and-loop straps as well as the rack cable manager?

Yes. They perform complementary jobs.

The rack manager establishes the broad route through the cabinet; a reusable hook-and-loop strap can then keep a local group of cables together where that is useful.

The important distinction is restraint rather than compression.

A modest strap keeps the bundle orderly and remains easy to reopen later; hauling everything tight until the cabling behaves like one rigid object rather defeats the serviceability the manager was there to provide.