I don't comb (or do anything) to my hair after diving until I'm taking a shower. Once I'm in the shower, I saturate it with conditioner, and only then do I comb it out. The comb then slides through easily with no tangle effect. After that I usually just rinse it --- I save shampooing for the end of the trip or at least only every four or five days or so. I figure the natural oils don't need to be taxed any more than they already are with diving.
After this routine, my hair is usually nicer after the dive trip then it was before (and this is salt-water diving). (I tend to have sort of dry/coarse hair.)
I've read that conditioner is not great for the reef, so I have never tried using it before diving. That said, the "conditioner to comb out in shower" method has been working well, so I've also never had a need to research it to see how true it is.
During the dive I usually use an off-center braid (on-center was hitting the regulator), which also helps to keep my mask strap from slipping down. I recently did a few dives with a hood (colder water), and wow, that was convenient. No tangles, no hair-to-mask-strap interference, and the mask strap stuck like glue.
I can see why people who dive a lot might consider "buzzing" long hair.