Yes but you need to time it so you don't get hit by aoe, lose the vanish and still have no pot reset. Also if you stay out of combat more than 4-5 seconds you should be losing more dps than you gain.
@Poison discussion
As far as I know, and I think I am repeating myself, mastery does not proc proisons, so why is this discussion still going on? With 5 stacks DP should be ticking an extra dmg each time you melee, on top of the dot tick(the way pala Censure does) but these ticks are far weaker than IP(maybe even half dmg?) because IP's ppm is alot higher, and these procs are also on a ppm. Using both weapons with DP or both weapons with IP is also a loss because poisons share hidden cooldown. In conclusion you should be using Instant poison on you mainhand because it's the biggest source of poison dmg, and because in mainhand it is guaranteed to get the maximum ppm obtainable out of it and DP on you offhand because the dot benefit outweighs the ppm of something like wound poison because the offhand still misses alot.
@Hit vs Haste discussion
Hit above melee cap benefits 2 things, one is the offhand(up to a cap of 27% which is unreachable and huge) hit chance and the other is poison hit chance up to the spell cap of 17% but these sources are so weak in comparison to the sources of damage empowered by haste that the whole thing is hilarious. Also it should be mentioned that above the melee specials hit cap(8%) mastery does not get any benefit whatsoever so hit loses alot of importance after the specials cap is reached.
Now why is haste good? because look at the dummy tests mentioned here, 2 of the best sources of damage are still SS and Eviscerate, in close competition with melee attacks, as long as this will remain haste will remain king because it directly affects how many SS and Evs we can do in the course of the fight
@Melee attacks issue
A big part of melee attacks dmg comes from the mainhand not the offhand, since the mainhand never misses, they are in terms of pure weapon dps the same but the offhand still misses. Further more the offhand often hits with glancing blows, it's something that cannot be avoided since glancings are not removable of the attack table and they do lower damage than regular offhand hits. This is because on the attack table glancings come after normal hits and are followed by criticals, it's also a reason why in certain patches a crit cap can be reached which represents the point where there are only normal hits, glancings and criticals going on for the offhand.
Because of these factors we have faster weapons in offhand, because at higher speed, they do more damage than a weapon with slower speed but same dps, because they hit more often, and the chance of those many hits to be regular dmg or crits improves significantly as there are more attempts. Theoretically slower weapons should come close to fast weapons but the fights are way to short overall to even come close to that point.