The short answer is: no one really knows. A lot of people here have very strong opinions. Some feel they are a sign of healing and return to normal sexual health. Others feel they are some kind of horrible recovery killing trauma. But there is no real "proof" one way or the other. From my perspective it seems like people believe whatever it is they are predisposed to want to believe in the first place. If one goes in believing wet dreams are bad the will feel horrible when they happen. If one feels they are no problem they won't have a problem if they have one.
I personally never had a problem with them. I knew going into abstinence that it was an either/or situation. If I didn't masturbate I was going to have wet dreams. So I saw them as validation, clear proof that I was succeeding in my commitment stop masturbating. So I felt pretty good about them. And yes, I did enjoy having a nice guilt-free orgasm now and then.
They also don't seem to have had any effect on my "healing" either. When I first began NoFap as a young man I had wet dreams every time I managed to successfully stay PM free. I still grew, matured and overcame being shy and withdrawn. I got out and met a nice girl, dated her and finally lost my virginity. Even with all the wet dreams, NoFap was still worked for me.