Will allowing a cable eye bolt to become overgrown damage the trees or must the cables be replaced?
Both trees are generally relatively short lived trees. Silver Maple has weak joints. You are eventually going to lose the tree. You may want to start a replacement tree 10 feet to the side.
However, the bolt being engulfed by the tree is no big deal. There may be issues with the flex and motion of the cable keeping a wound open. You may want to fill it with some flexible material. (I'd suggest silicone based window caulking)
The bolt IS a big deal to someone taking down the tree. Hitting a bolt with your chainsaw is not a good start to the day.