I like the idea, myself. I know I could worry and wonder what sort of person he is, and whether they'd dislike him, or whatever. But the fact he's been in the same boat as us, seeking fertility treatment, makes me feel reassured. He will have tackled some of the same questions of how to talk to his children about their origins. It might even be that they were conceived with donor eggs (we don't know).
I'm hoping that, if I do IVF, I'll be able to donate eggs myself, and if so, it would also be something I'd discuss with children at an age-appropriate time. So hopefully, they'd grow up thinking of it as unremarkable.
It helps that we do know other people in the same situation. A woman in my NCT group has a baby with a donor egg (though AFAIK she's only mentioned it to me and not the others). My close friend has a baby that is biologically hers and her partner's, but her partner doesn't live with her and won't be a conventional 'dad' figure. Our baby's cousin is an IVF baby. DP's mum is adopted. Etc. etc. Lots of different types of family relationships to compare to. I think that will help.
I suppose it also makes it easier that there is unlikely to be a big reveal that DP and I are not, in fact, both their biological parents. 
I am feeling nervous if we can't manage to use the same donor DP used, for me, though. Because I really don't want the guy who wrote his children the CV! Just imagine being 18 and perhaps rather fed up at school, and hearing your biological father banging on about his degrees!