I have mine hanging in the sump and don't clamp the hose fitting on either reactor fixture. I do clamp the other side of the female coupling. Been doing this for over two years and never had a leak. I do this so I can readily remove the reactor to change the media. I have minimal flow going through all of mine, probably 110 gpm max.
All of this said, if mine hung outside the sump I'd probably clamp them also, better safe then sorry.