Yes, sort of. Weapon speed for both mainhand and offhand has no effect effect on rage generation. As long as you are dealing white strikes (or taking hits), you are generating rage. Note that offhand white strikes generate less rage, though I'm not sure exactly how much less. I think it's 50%.
As far as DPS is concerned, you should understand how DPS and white strikes work. All Warrior skills, with the exception of some elites and such, are based on mainhand weapon DPS. This is the Weapon Damage/Weapon Speed (weapon speed is the number of seconds between each hit, or white strike). This is because skills share a global cooldown of 1 second. White strikes are based on your Weapon Damage, not DPS, and hit at weapon speed, not each second. Because of this, white strike DPS is the same as skill DPS. The difference is that skill DPS is more consistent, as it hits every second, and of course skills deal more than 100% DPS more often than not. Offhand weapon only does white strikes, so weapon speed only effects it's frequency of hits, but not DPS. If you're doing a lot of killing mobs where the fight only lasts a second or two, a high Damage weapon, like a hammer, would be better because if you only get one white strike in, it'd best be a strong one. For something like bosses where you're fighting for several seconds or more the offhand DPS is what counts. Overall, the offhand isn't going to be making a huge difference Damage wise. You could invest in a powerful offhand hammer for grinding, but the difference would be minimal in most cases, and hardly worth it.
For the most part, you should just get the highest DPS weapon you can for offhand, and stat-tier it. Swords and axes tend to be best, and you should also look at the ghost stats on the weapon. Speed, for the most part, is insignificant.