Can some contacts actually slow or control nearsightedness?

Not really: Poorly fitting contact lenses (too tight) of the rigid type (gas perm or hard lenses) can flatten the curvature of the eye and temporarily reduce nearsightedness when the lenses are first removed. But the eye soon springs back to its original shape and the changes are only temporary. Orthokeratology (ortho-k) is an optometric method where lenses intentionally do this - not recommended!

Yes: Rigid contact lenses can stabilize the cornea and reduce the progression of nearsightedness. That being said, they are rarely prescribed for this purpose. Most people wear the contacts they like and change the prescription as their eyes change.