I might have actually brought up Chomp-in-Sun :O
anyway, if Sand Veil was still allowed, then of course at least I would use it over Rough Skin, just like some people still use Kingdra to counter Rain. Except Garchomp is already hard enough to counter as it is.
You also bring up a good point, alk, about Sun. If Sand Veil+Sand complex ban was underwent, well Garchomp being so popular in Sun would support my idea. There you have it- the perfect counter to Sand, one that resists Rock types moves, uses enemy sand to transform itself into a Dancing monster, and punching massive holes in the opponent and then letting Chlorophyll sweepers do their thing. Another reason why even a complex ban wouldn't work. If Sun hates Sand, Garchomp loves Sun, and Sand hates Garchomp, wouldn't that make Sun all the more broken now that one of it's best counters is countered?
What I really meant by #2 was why I would consider taking the risk of Sand Veil even without my own Sand. Rough Skin is a great ability, but if it were allowed, the added evasion that comes with SV is just too good to pass up, even if 84% of the time (as you said) Sand isn't up. Having no Sand doesn't exacly cripple Chomp either, so naturally SV would be preferred over RS, if it were allowed. But hey, that's just my input.
EDIT:
@ Super Mario Bro:
sorry, but I fail to see how the OU metagame is 'almost unplayable now'. Sure, there's been a power creep, but it's not as if there are any particular pokemon that are so powerful that they just tear everything apart. There really isn't much that is broken right now, other than Sand Veil, which is being taken into consideration right now. Garchomp may seem powerful, but it's still walled by Skarmory and Gliscor, and very susceptible to multi-hit ice moves. It's also great set-up bait for (yes) Cloyster, whose massive Defense will allow it to take an EQ and OHKO back with Icicle Spear. Garchomp is also a great 'cleansing' for the OU meta- it's a great answer to Tornadus, Terrakion, and the multitude of therians because it has just enough power and speed, and bulk to do work against them. The scarf set is an excellent answer to Terrakion and all therians because it outspeeds Thundurus-T by 1BP. That's real speed creeping.