Swift Numerics doesn't use Accelerate at present, because it doesn't yet include API that would benefit from using Accelerate. It will likely use some pieces of Accelerate in the future, but only the pieces that have alternative open-source implementations available (BLAS, LAPACK, maybe FFTs, ...), because Swift Numerics is intended to provide a uniform cross-platform API.
I should note that the vDSP, vForce, and Quadrature API in Accelerate all became vastly easier to use from Swift in macOS 10.15 / iOS 13.0 / tvOS 13.0 / watchOS 6.0. There's further work to be done, but the Accelerate team has done a great job improving them already. E.g.:
let a: [Float] = // ...
let b: [Float] = // ...
// Create new array with c[i] = a[i] + b[i]
var c = vDSP.add(a, b)
// Or update a contiguous collection with the right element type in-place
// (this works out of the box with Array and UnsafeBufferPointer and a
// Slice of any conforming type, but you can add your own conforming
// types to `AccelerateBuffer` too):
vDSP.subtract(a, b, result: &c)