I'm someone who is merely a customer when it comes to scuba. Personally, I think that the relationship you describe between Deep Six and yourself is exactly the sort of thing I'd like to see mentioned in your bio or preferably signature line. I tend to have a favorable opinion of Deep6 based on my experiences with the guy when he was with another well regarded company, but I digress... I think you should disclose the relationship in an easy to find location.
While I would normally agree with this, the rest of @RainPilot 's post states "By removing that link, I now have nothing to gain from a referral so hopefully that will un-muddy the waters."
I agree with this fully. He can't receive compensation for anything if he doesn't supply the link that would let Deep Six know how a customer found them and in turn allow them to push the commissions to him.
If he doesn't post the link there is no financial gain from a positive review and therefore, IMO, is just like if I were to post a review of a product.
BTW, I have run across the Deep Six people on more than one occasion and I can tell you that from how they treat customers (I am not one but have read many threads about this and know some of their customers), how they have treated me as a possible future customer ( I am leaning towards getting a pair of their fins) and all the reviews I have read on their product, they are a business I would be happy to give my money to and I know for a fact I will one day buy something from them just based on how they conduct themselves in a public forum.