Knowing him, I think he'd rather it be someone he knows then somebody random.
Oh? Then why bother with "no names" at all thing then?
They are rather annoyed/bored with each others sexual/emotional needs which is why they're trying poly.
Great. Common pitfall -- Opening when foundation is not strong, seeking someone ELSE to fix whatever is broken between them. They could go take some sex ed classes, reconnect, break up -- SO many other things than OPEN and invite new people into their iffy.
Again -- you are responsible for your own best healths. You choose as you wish. But this one? I'd pass if it were me. Their willingness to be adding more
people to something that is sounding kinda wobbly doesn't sound to me like THEY are tending their own best healths or the health of their relationship very well.