What the fuck were the swift water rescuers going to do in the dark of night with everything being swept away? We aren’t talking about a bunch of people stranded that they could locate and extricate.
they aren’t going into that water to catch whatever people happen to flow to them. It would have been over and they’d be a few more eyes looking for survivors in the morning.
eta: that’s why all this bullshit from all over about being ready is such bullshit. They couldn’t have saved any during the event, they didn’t save many after the event. The time to save lives was before the event. And since they, more than once, made the conscious decision to not have the siren flood warning system that others have, and didn’t have any kind of warning system besides apparently door knocking, in an area called flash flood alley in which they claim to be experts at handling floods, it falls on them to have a legitimately actionable plan with a good chance of success. And that plan wouldn’t include ignoring weather warnings.  
people still would have died- there were too many to locate. (Loud sirens could mitigate this issue derp) but they could have saved lives with appropriate action in the hour or so before the event unfolded.