The BECs of those particular ESCs are 3 amp switching regulators so they should be OK to power one or two servos each (depending on the servo’s power requirements).
@Dave84 likely has a good reason not to trust BECs on ESCs but I personally use these BECs in several of my quads and airplanes.
Some ESCs use linear regulators for the BEC. A linear regulator will heat up much more than a switching regulator. I wouldn’t use a linear BEC for a servo.
In general you don’t want to connect multiple BECs in parallel. Only one ESC’s power lead should connect to your flight controller. Parallel BECs don’t always blow up but this happens often enough that I think it’s a really bad idea to use them in parallel.
I personally divide up the 5V power requirements in my aircraft so the power is distributed amount the multiple BECs. In an airplane, I’ll use the BEC on the right wing motor’s ESC to power the right wing’s servo(s).
As @Dave84 suggests, you should check to make sure the BECs can handle the power requirements before putting the aircraft in the air. I doubt you have an oscilloscope based on your self described “lackluster” knowledge of electronics. Instead you can try other methods of testing the BECs such as cycling the servos multiple times and making sure they behave well. Make sure to feel the BEC circuit on the ESC to see how hot it gets. Some electronics can operate safely while being too hot to touch but in general, it’s a bad sign when electronics get really hot.