Denial in ADHD I believe is not actually an ADHD problem. For guys, anything that looks as though they are lacking in something or are unable to control in their life, they will attempt to deny. There is even an scientific article detailing how men actually have very healthy attitudes towards improving on depression, yet are unlikely to seek help from a therapist or from others. You can imagine what potentially being listed as having ADHD ('deficient', 'disorder') will do to them. What will make them more likely to seek help is if you reword it. Rather than suggest a therapist, suggest a support group. Rather than saying seek help, say gain more control of their own life.
In my own life, this has helped me quite a lot. By seeing my ADHD as something to be taken advantage of, I have made a lot of progress. Rather than seeing it as something that impedes my ability to do things (although I am aware it can), I have seen it as an obvious route to making my life better. In other words, I now know exactly where to focus my attention and awareness on in order to make myself better.
Believe it or not, in psychology it's actually well a widely accepted view that men and women should be treated psychologically differently. Not only are there swathes of evidence for it, it is also acknowledged as a problem in psychology (i.e. therapists struggle to overcome the view that they should treat them differently). In terms of therapy, men want solutions while women want to be listened to. Though my earlier paragraph may explain why men are more likely prefer support groups more than therapists, it can also hint at how a woman with ADHD might overcome denial. For example, listening to her problems and getting her to reveal them might give them incentive to try to improve themselves more. Just something to consider for those with ADHD wives.
Anyhow, It's this mindset of trying to be better and trying to take advantage of my ADHD which set me off on trying to improve and which might help others overcome their denial of their problems. As always, there's always a next step. We know we'll need the persistence to have to fail multiple times before finding a workable solution. As the quote attributed to Thomas Edison says, 'I have not failed. I have simply found 10,000 ways that don't work'.