At the time of this writing, nothing beyond the 6.1.0 patch has been released, so the answer to the above question is a resounding “no”. While their amiibo are scheduled to release on January 17th, as of yet there is no functionality for these amiibo in the game. But how do we know?
Amiibo researchers (I’m not one of them) have discovered that certain sections of an amiibo’s .bin data correspond to their character and series, and that’s how the amiibo is identified. For example, a Super Mario series Mario would be [Mario, Super Mario], while a Gold Mario would be [Gold Mario, Super Mario]. Then, a Super Smash Bros Mario would be [Mario, Super Smash Bros]. These listings are formatted in the data with a simple numerical listing.
As it happens, each fighter has its unique number inside of its series listing, typically according to some number important to their series. However, Echo Fighters are listed differently, sharing a number with their main fighter but with a slightly different notation. Knowing this, we can start with the .bin file of a currently released amiibo and then edit it so that we’re starting with the Echo Fighter version of that amiibo.
In other words, we’ve edited a [Simon, Smash Bros] and [Samus, Smash Bros] amiibo file to produce [Simon*, Smash Bros] and [Samus*, Smash Bros] which scans in as Richter and Dark Samus.
We’re 100% certain that they were produced correctly (this isn’t the first time someone has created an amiibo before their release), so we can be confident that Dark Samus and Richter’s amiibo functionality is currently not in Smash Ultimate.