> collision speeds would be measured in millimeters per second, and forces in millinewtons.
What satellite ending their end of life, and already in orbit do you suggest are capable of such delicate manoeuvring? This is a very delicate task you are describing, and most satellites are simply not designed for it.
> The main risk is that the satellites touch at the 'wrong angle' or blocking an attitude control thruster.
If someone tries this, the most likely outcome is that the satelites wizz by each other without ever touching. If you somehow manage to aim the "pushing" satellite accurately enough at the "stranded" satellite they would most likely collide at anything from a few hundred meter/s to a few of km/s depending on the orbital arrangements.