In terms of teeth, after a couple of crunches, dry food is the same as wet and just as likely to cause teeth problems (the exception is Hill's T/D, which is special process to fracture in a certain way).
Somtimes traits are controlled by the same gene, it's just the way the resulting protein acts in different cells. Other traits are controlled by genes located on the same chromosome and don't get separated when cross-over (gene swapping) occurs during the production of sex cells. The closer the genes are the more likely they are to stay together. This is why some seemingly unrelated traits go together.
To help prevent urinary tract problems, keep your cat well hydrated. This will dilute any potential irritants and flush them out. The premium diets are better for keeping you cat's bladder happy as well. There are less useless ingredients that might harm his bladder. If putting waten in his dry food gets him to drink more, that's good. Just split his totasl daily ratio of food into two parts and give some with water and the rest without. Just try to make sure he gets more than one feeding per day, it helps prevent the peaks and troughs in blood sugar that predisposes animals (including humans) to diabetes and other related problems.