1. If a robot overcomes an obstacle in the evacuation zone, does the team earn 10 points?
No. For reference, please check:
3.5.2 A robot is considered to have successfully navigated a hazard (obstacle/intersection/dead end/speed bump/gap) when it has traversed the tile where it was placed without human intervention.
As there are no tiles in the evacuation zone, there will be no points awarded for navigating around an obstacle in the evacuation zone.
2. Do obstacles in the evacuation zone be fixed?
Any obstacle may or may not be fixed to the floor:
1.4.6 A robot is expected to navigate around obstacles. The robot may move obstacles but it should be noted that obstacles may be very heavy or fixed to the floor. Obstacles that are moved will remain where they moved to, even if that prevents the robot from proceeding.
3. How many obstacles can be placed in the evacuation zone? Are there more than four obstacles in the evacuation zone?
There is no rule on that. It is up to the field designer / the organizers to place a number of obstacles in the evacuation zone that makes sense (which includes that there may be zero obstacles in the evacuation zone).
Hope that my answers help you,