Does the Services module implement caching on GET requests?
No, the Services module does not support caching on GET requests:

http://cgit.drupalcode.org/services/tree/resources/node_resource.inc?h=7.x-3.x#n253

As you can see, each time the resource's callback function is invoked, it makes a call to node_load(). You can use the Services API to preprocess/overwrite the resources to implement caching though:

http://cgit.drupalcode.org/services/tree/docs/services.alter.api.php?h=7.x-3.x