On Life Insurance (brand new AllState policy), my diving had a negligble impact of $10 per month.
On Health Insurance (Blue Cross), there are no exclusions for recreational diving in the policy.
However based on expereince (my wife has some significant health issue, so we had plenty of experience) the insurance companies will nickel and dime you to no end. Their nickels and dimes have lots of zeros, so these can really hurt. An example, they will only pay what THEY think is reasonable and customary charges. When you start dealing with poor commincations with forgein providers plus it ignorance of diving med by the insurance company, you are all most assured of a major screw-up.
Now for the fun part. In the US, typically if you have insurance, they treat first, then bill you. When traveling, it is often pay first, then treat. The providers are not going to deal with the insurance company, you are! You pay, then 2-3 months later you start fighting the insurance company over the screw-ups to try to collect what is due you - Good luck you will need it. They are experts at finding loopholes to deny payment and most of us are total newbs at the game.
IMO - The actual insurance $$$ paid out by DAN is probably very modest compared to the total amount of premiums they collect. By itself, I would almost consider it a rip-off similar to extended warrenties on goods. BUT... the key benefit is having experienced insurance professionals in your corner. Once there is a claim, they are very motivated to make your insurance company pay its full due since it reduces their liability. Their experience in dive med can all be to your benefit. You basically set up a situation where the 2 insurances companies can fight it out instead of your versus a single company. Better odds!
So in the end - I buy DAN - never used it - hope I never need to.