From what I've read in different reviews controling x10 from this would be no different the controling from any of the show devices. As long as Alexa can see and control your x10 devices you should beable to add them to this.
I've looked at many different ways to control x10 with Alexa, all require some sort of extra hardware.
As for the echo hub I suspect it will at launch or shorty after display unwanted adds just like all the shows. This has resulted in many users giving up on the shows for this reason or the fact that setting get reset to defaults on updates.