I cannot see how any good can come of her birth father meeting the boyfriend's parents, nor do I see any reason why an uninvolved birth father has any need to meet them.  I would advise against it.  I also wouldn't be happy about the boyfriend's parents meeting the deadbeat birth father before they meet the man who has raised her.

Your DD is 15. I would not get involved in her relationship with BF or his odd request to meet Boyfriend's parents. I would discuss your concerns with DD, that having BF meet them may not be a great impression due to his instability, but that you support DD's decision to do what she pleases regarding BF meeting the parents. I think that demonstrates that you value DD's autonomy to manage her own life. If BF blows it or makes a fool out of himself, its on him and DD may learn to not involve BF in those types of things. Plus, it removes you from any backlash from DD or BF if things don't go well. 

I get not wanting to keep your DD from having some kind of relationship with her father.. BUT.. I think it's super important that she also isn't exposed to an active drug user/addict.  Honestly.. she wouldn't be the first child who ended up getting into drugs with their parent providing..or unwittingly providing the contraband.  Clearly with her father's genes.. she is likely more predisposed to become addicted to things.. it can have a genetic component.

So.. without assurance that he is clean and in a good place?  I don't think you should actually encourage much contact.  In fact.. if he doesn't have an active custody order.. I might want that in place with some kind of assurance he is not using drugs as a condition of her being able to see him.

I actually don't think she is obligated to introduce her BF to him.. OR his parents.  Honestly, I think that sounds like a fairly bad idea ... she barely knows him herself at the moment.. she doesn't need to complicate it.. 

and as LD said.. you can be the one to use as an excuse here.. 

We couldn’t keep Spawn shielded from Meth Mouth, the courts joyfully did everything they could to keep Spawn connected to her toxic drug addict mother.  Spawn was exposed to very bad things that no kid should be.  Seeing her mom arrested, sharing a room with her while she screwed guys behind a sheet strung up, raising her brother while meth mouth would get high and pass out, and lying for her mom while she harbored a fugitive.  That's just a very small bit of what she endured, and that was just on "visitation" time.  Thankfully the courts have not forced you to hand your daughter over to this POS for weekends and weeks at a time.  Personally from seeing firsthand how bad it really is for the kids, keep our daughter away from this crap!

As DS/DD are more likely to do drugs / get hooked on drugs then DS/DD of familys that don't have drug use.   That a common medical excepted theory.  So exposing your DD to the ex and his drug use is not a good idea.  No reason to temp her.  You ex wanting to meet her BF family is out of the question,

Can You ex come off normal, it is he and BF parents going to exchange prision storys,  Does he has that drugy look.  drugy Speech.  Is he going to ask them for money?  Is your DD ,BF parents going to tell there son. He nuts for dating your DD ?

I dealt with the crazy, alcoholic ex. At his age anybody could see he was a professional alcoholic.  He never support his kids, or saw them. He could not be sober enough to pick them up,  He know my DW would call the police for a breathalyzer test .   Fortunately for all he drank himself to death when kids were 11 .

Bad part mt DW wanted us to pay for his funeral.  You know for the kids  I said I would kick in the only  $35 of support he ever paid.  Did not need his $35  even though it's was for ghetto kids