If there is any boats in lake #1 when the pumps are hit, then it is automatic that the Tower 1 operator has the jump in the water. Their job is to move the boats around so that the guests can climb from one boat to another so they can use the ladder to get out of the trough. Also, if pumps are hit and there is any boats past lake #2 (inside the shed), then they engage a gate that will push the boats into the reservoir. At that point an operator (4-7 operator) has to jump in and go get them because they are literally just floating around in a giant pool. The operator will swim the boat over to an platform in the back where the guests will be evacuated.
When pumps are hit- all of the water drains out of lake #1 and section 1 and 2 and part of 3. There will still be water in lake #2, so they will still be able to move the boats into position for evac. The pumps can be restarted with guests in the boats in lake #2, so a lake 2 evac is more rare.
So yes, they actually do get in the water when the pumps are turned off. Usually it is the 4-7 operator and tower 1 operator that do. Tower 3 will assist only if they are needed. Which, generally, they arn't because Canyon has not run their max # of boats in a LONG time. Also, the park does mock evacuations usually at the beginning of the season, so they will dispatch the boats with team members on board and practice evac's from various spots.