Currently, Graph.vertices() and Graph.edges() can take a Vertex or Edge object as arguments respectively as filters. Unless it is somehow deemed necessary by the implementation, there is no need to re-query those objects and they can simply be returned as the caller already has them. TinkerGraph currently does this as part of the reference implementation.
Of course, TinkerGraph doesn't currently account for a Detached/Reference implementations where it would probably make more sense to re-query to get TinkerVertex/Edge into the Traversal. This is mostly an issue to recall the need to build appropriate tests for this to ensure consistent operations.
Also consider implications for StarGraph and related Detached/Reference implementations as it pertains to tests.