It's going to depend on the radio/tuner. I've got a portable ham radio (Icom IC703+) with a built-in tuner that is designed for a coax output. In this case the tuner's tuning-range is fairly small, and it is designed to compensate for antennas that are slightly out of tune. This is useful if you are putting up quick dipole and don't want to trim it in.
On the other hand, my boat
radio and tuner do indeed work
with an unshielded wire feeding the backstay.