first, don't power the servos from the MEGA's 5V output. That might draw too much current for your MEGA and lead to a crash. Servo should be powered separately and GND shared with the MEGA.
the typical wiring of a voltage adapter is as such:
you have on one side the 3.3V I/Os and on the other side the matching 5V I/Os. The correspondance goes both ways. So connect Tx and Rx of the ESP-CAM to the 3.3V side and Rx1 and Tx1 of the MEGA on the other side (so that Rx is connected to Tx and Tx to Rx). connect GNDs and suitable voltage on both sides.
Look if Serial2 is available for the ESP32-CAM. That will give you a second UART to connect to your MEGA (use Serial1 for example so that the MEGA can also have it's Serial line free for upload and debug)