Actually not. The true target/match rounds (Eley, Lapua, Federal Match, etc) are all subsonic at around 1050 fps. They loose velocity when barrels lengthen much beyond 18". When shot through very long target guns, the velocity and 'bang' are significanty reduced. The true target rounds do function just fine in most semi-autos. It would, of course, pay to test each type of subsonic ammo in YOUR gun to make sure.
CBs are a totally different story. They have MUCH reduced velocity (750 to 850 fps) and will not function in semis. While these are definately subsonic, they are not what is usually refered to when the 'subsonic' term used. These are not target rounds (plinking, yes) and are, quite frankly, very inaccurate in comparison to true target rounds or what is often labeled subsonic hunting rounds (Remington subsonics, CCI subsonics, and the new Winchester subsonics). These, again, will have velocities in the 1050 to 1100 fps.
I just interrupted this typing to step outside the door and test three subsonic makes (Lapua, CCI, and Eley - all hollow points) in my 10/22. I usually shoot them from a bolt action. They functioned fine in the 10/22 and all hit what I was aiming at about 85 yards across a ravine by my drive.
Of course, we really don't know what the OP was referring to when he stated 'subsonic' ammo. Is he asking about the 1050 fps hunting or target subsonics (most likely), or is he referring to CB caps or Aguilla Colibris. Neither the CBs or the Colibris are good for anything but informal, close range plinking. I shoot them off my deck sometimes. Yes they are fun, but they are not for any survival situation unless we are worried about attacking mice and rats.
