[Tiax]

Dorn was recruited, but did not join the party after his dialogue. I noticed that Dvaradime had an interjection with Dorn, so after a few more tries experiencing the same issue I dropped Dvaradime and was able to recruit Dorn.

[Lava]

I am sorry, but I think it may be some interaction with another mod you're experiencing. I just tested it -- both the version in which Dvaradime interjections and PC knows Dorn, and the path in which we state we've just met Dorn for the first time. Dvara interjects and Dorn just joins the group: