RC servo suitable for robot arm or not
A servo motor means it has feedback, you have the motor which does the actuation, and you have the feedback system that reads back where the servo is positioned and trims the position of the motor to make them align, 

Most use either a potentiometer, an encoder wheel and 2 or more sensors, or a hall effect rotation sensor, the goal is that is is able to read back in where the rotor is positioned so that it can make sure it matches what is set,


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a servo motor without an integration term would not be desirable in most cases, as this is what corrects small offsets, to make sure where it ended up is exactly where you desire, due to how noisy this position measurement tends to be, I suspect most would not use derivative, so a PI controller. 


This should mean that if you nudge the servo horn it should come back to the same position each and every time, and to be very hard to turn if you try and force it, this would be it correcting for steady state errors. 

The internal servo controllers are usually "tuned" to be stable over there speed and weight limits, meaning they should not oscillate. what this usually means is if you find the slowest and least reactive P and I settings for those ranges, while it makes the response slower, it means that there is no point during operation where it is at risk of oscillation, 


Inverse kinematics give you what angles you need each motor to be for a motion path, however you need to build the speed and inertial limits in to your model, e.g. extending an arm on a robot, the elbow joints speed is not linear over that time period, and you will need to slow the speed of that motion to match the slowest motor, any faster and it will not line up with what you expect, equally if you put too much load on a motor by asking it to accelerate faster than its weight limit, it will also not match your expectation.


Other tricks to make things as stable as possible will be to slice your motion path up into many small steps, the larger a step you ask the servo to follow, the less control you have over how it gets to that step, and means you have to start correcting for the motors internal control system, instead try and make your own kinematic control system closer to a least disturbance control system, where it deliberately runs a little slower than the control loops it feeds to make sure your never pushing things to a point where they can oscillate.